diff --git a/go.mod b/go.mod
index 7e94a0a32..cdf2af233 100644
--- a/go.mod
+++ b/go.mod
@@ -6,6 +6,7 @@ require (
 	github.com/btcsuite/btcd v0.22.0-beta
 	github.com/gorilla/websocket v1.4.2
 	github.com/hashicorp/golang-lru v0.5.4
+	github.com/holiman/uint256 v1.2.0
 	github.com/mr-tron/base58 v1.2.0
 	github.com/nspcc-dev/dbft v0.0.0-20210721160347-1b03241391ac
 	github.com/nspcc-dev/go-ordered-json v0.0.0-20210915112629-e1b6cce73d02
diff --git a/go.sum b/go.sum
index a38e4b761..7b06b7467 100644
--- a/go.sum
+++ b/go.sum
@@ -128,6 +128,8 @@ github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/ad
 github.com/hashicorp/golang-lru v0.5.4 h1:YDjusn29QI/Das2iO9M0BHnIbxPeyuCHsjMW+lJfyTc=
 github.com/hashicorp/golang-lru v0.5.4/go.mod h1:iADmTwqILo4mZ8BN3D2Q6+9jd8WM5uGBxy+E8yxSoD4=
 github.com/hashicorp/hcl v1.0.0/go.mod h1:E5yfLk+7swimpb2L/Alb/PJmXilQ/rhwaUYs4T20WEQ=
+github.com/holiman/uint256 v1.2.0 h1:gpSYcPLWGv4sG43I2mVLiDZCNDh/EpGjSk8tmtxitHM=
+github.com/holiman/uint256 v1.2.0/go.mod h1:y4ga/t+u+Xwd7CpDgZESaRcWy0I7XMlTMA25ApIH5Jw=
 github.com/hpcloud/tail v1.0.0/go.mod h1:ab1qPbhIpdTxEkNHXyeSf5vhxWSCs/tWer42PpOxQnU=
 github.com/inconshreveable/mousetrap v1.0.0/go.mod h1:PxqpIevigyE2G7u3NXJIT2ANytuPF1OarO4DADm73n8=
 github.com/jessevdk/go-flags v0.0.0-20141203071132-1679536dcc89/go.mod h1:4FA24M0QyGHXBuZZK/XkWh8h0e1EYbRYJSGM75WSRxI=
diff --git a/pkg/core/mempool/mem_pool.go b/pkg/core/mempool/mem_pool.go
index 7e1bb98ef..e0790464e 100644
--- a/pkg/core/mempool/mem_pool.go
+++ b/pkg/core/mempool/mem_pool.go
@@ -3,11 +3,11 @@ package mempool
 import (
 	"errors"
 	"fmt"
-	"math/big"
 	"math/bits"
 	"sort"
 	"sync"
 
+	"github.com/holiman/uint256"
 	"github.com/nspcc-dev/neo-go/pkg/core/mempoolevent"
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/util"
@@ -50,8 +50,8 @@ type items []item
 // utilityBalanceAndFees stores sender's balance and overall fees of
 // sender's transactions which are currently in mempool.
 type utilityBalanceAndFees struct {
-	balance *big.Int
-	feeSum  *big.Int
+	balance uint256.Int
+	feeSum  uint256.Int
 }
 
 // Pool stores the unconfirms transactions.
@@ -164,8 +164,7 @@ func (mp *Pool) tryAddSendersFee(tx *transaction.Transaction, feer Feer, needChe
 	payer := tx.Signers[mp.payerIndex].Account
 	senderFee, ok := mp.fees[payer]
 	if !ok {
-		senderFee.balance = feer.GetUtilityTokenBalance(payer)
-		senderFee.feeSum = big.NewInt(0)
+		_ = senderFee.balance.SetFromBig(feer.GetUtilityTokenBalance(payer))
 		mp.fees[payer] = senderFee
 	}
 	if needCheck {
@@ -173,23 +172,26 @@ func (mp *Pool) tryAddSendersFee(tx *transaction.Transaction, feer Feer, needChe
 		if err != nil {
 			return false
 		}
-		senderFee.feeSum.Set(newFeeSum)
+		senderFee.feeSum = newFeeSum
 	} else {
-		senderFee.feeSum.Add(senderFee.feeSum, big.NewInt(tx.SystemFee+tx.NetworkFee))
+		senderFee.feeSum.AddUint64(&senderFee.feeSum, uint64(tx.SystemFee+tx.NetworkFee))
 	}
+	mp.fees[payer] = senderFee
 	return true
 }
 
 // checkBalance returns new cumulative fee balance for account or an error in
 // case sender doesn't have enough GAS to pay for the transaction.
-func checkBalance(tx *transaction.Transaction, balance utilityBalanceAndFees) (*big.Int, error) {
-	txFee := big.NewInt(tx.SystemFee + tx.NetworkFee)
-	if balance.balance.Cmp(txFee) < 0 {
-		return nil, ErrInsufficientFunds
+func checkBalance(tx *transaction.Transaction, balance utilityBalanceAndFees) (uint256.Int, error) {
+	var txFee uint256.Int
+
+	txFee.SetUint64(uint64(tx.SystemFee + tx.NetworkFee))
+	if balance.balance.Cmp(&txFee) < 0 {
+		return txFee, ErrInsufficientFunds
 	}
-	txFee.Add(txFee, balance.feeSum)
-	if balance.balance.Cmp(txFee) < 0 {
-		return nil, ErrConflict
+	txFee.Add(&txFee, &balance.feeSum)
+	if balance.balance.Cmp(&txFee) < 0 {
+		return txFee, ErrConflict
 	}
 	return txFee, nil
 }
@@ -323,7 +325,7 @@ func (mp *Pool) removeInternal(hash util.Uint256, feer Feer) {
 		}
 		payer := itm.txn.Signers[mp.payerIndex].Account
 		senderFee := mp.fees[payer]
-		senderFee.feeSum.Sub(senderFee.feeSum, big.NewInt(tx.SystemFee+tx.NetworkFee))
+		senderFee.feeSum.SubUint64(&senderFee.feeSum, uint64(tx.SystemFee+tx.NetworkFee))
 		mp.fees[payer] = senderFee
 		if feer.P2PSigExtensionsEnabled() {
 			// remove all conflicting hashes from mp.conflicts list
@@ -420,7 +422,7 @@ func (mp *Pool) checkPolicy(tx *transaction.Transaction, policyChanged bool) boo
 // New returns a new Pool struct.
 func New(capacity int, payerIndex int, enableSubscriptions bool) *Pool {
 	mp := &Pool{
-		verifiedMap:          make(map[util.Uint256]*transaction.Transaction),
+		verifiedMap:          make(map[util.Uint256]*transaction.Transaction, capacity),
 		verifiedTxes:         make([]item, 0, capacity),
 		capacity:             capacity,
 		payerIndex:           payerIndex,
@@ -507,8 +509,7 @@ func (mp *Pool) checkTxConflicts(tx *transaction.Transaction, fee Feer) ([]*tran
 	payer := tx.Signers[mp.payerIndex].Account
 	actualSenderFee, ok := mp.fees[payer]
 	if !ok {
-		actualSenderFee.balance = fee.GetUtilityTokenBalance(payer)
-		actualSenderFee.feeSum = big.NewInt(0)
+		actualSenderFee.balance.SetFromBig(fee.GetUtilityTokenBalance(payer))
 	}
 
 	var expectedSenderFee utilityBalanceAndFees
@@ -541,13 +542,10 @@ func (mp *Pool) checkTxConflicts(tx *transaction.Transaction, fee Feer) ([]*tran
 			conflictsToBeRemoved = append(conflictsToBeRemoved, existingTx)
 		}
 		// Step 3: take into account sender's conflicting transactions before balance check.
-		expectedSenderFee = utilityBalanceAndFees{
-			balance: new(big.Int).Set(actualSenderFee.balance),
-			feeSum:  new(big.Int).Set(actualSenderFee.feeSum),
-		}
+		expectedSenderFee = actualSenderFee
 		for _, conflictingTx := range conflictsToBeRemoved {
 			if conflictingTx.Signers[mp.payerIndex].Account.Equals(payer) {
-				expectedSenderFee.feeSum.Sub(expectedSenderFee.feeSum, big.NewInt(conflictingTx.SystemFee+conflictingTx.NetworkFee))
+				expectedSenderFee.feeSum.SubUint64(&expectedSenderFee.feeSum, uint64(conflictingTx.SystemFee+conflictingTx.NetworkFee))
 			}
 		}
 	} else {
diff --git a/pkg/core/mempool/mem_pool_test.go b/pkg/core/mempool/mem_pool_test.go
index a7e73839e..20d571953 100644
--- a/pkg/core/mempool/mem_pool_test.go
+++ b/pkg/core/mempool/mem_pool_test.go
@@ -7,6 +7,7 @@ import (
 	"testing"
 	"time"
 
+	"github.com/holiman/uint256"
 	"github.com/nspcc-dev/neo-go/internal/random"
 	"github.com/nspcc-dev/neo-go/pkg/core/transaction"
 	"github.com/nspcc-dev/neo-go/pkg/network/payload"
@@ -268,8 +269,8 @@ func TestMemPoolFees(t *testing.T) {
 	require.NoError(t, mp.Add(tx1, fs))
 	require.Equal(t, 1, len(mp.fees))
 	require.Equal(t, utilityBalanceAndFees{
-		balance: big.NewInt(fs.balance),
-		feeSum:  big.NewInt(tx1.NetworkFee),
+		balance: *uint256.NewInt(uint64(fs.balance)),
+		feeSum:  *uint256.NewInt(uint64(tx1.NetworkFee)),
 	}, mp.fees[sender0])
 
 	// balance shouldn't change after adding one more transaction
@@ -280,8 +281,8 @@ func TestMemPoolFees(t *testing.T) {
 	require.Equal(t, 2, len(mp.verifiedTxes))
 	require.Equal(t, 1, len(mp.fees))
 	require.Equal(t, utilityBalanceAndFees{
-		balance: big.NewInt(fs.balance),
-		feeSum:  big.NewInt(fs.balance),
+		balance: *uint256.NewInt(uint64(fs.balance)),
+		feeSum:  *uint256.NewInt(uint64(fs.balance)),
 	}, mp.fees[sender0])
 
 	// can't add more transactions as we don't have enough GAS
@@ -292,8 +293,8 @@ func TestMemPoolFees(t *testing.T) {
 	require.Error(t, mp.Add(tx3, fs))
 	require.Equal(t, 1, len(mp.fees))
 	require.Equal(t, utilityBalanceAndFees{
-		balance: big.NewInt(fs.balance),
-		feeSum:  big.NewInt(fs.balance),
+		balance: *uint256.NewInt(uint64(fs.balance)),
+		feeSum:  *uint256.NewInt(uint64(fs.balance)),
 	}, mp.fees[sender0])
 
 	// check whether sender's fee updates correctly
@@ -302,8 +303,8 @@ func TestMemPoolFees(t *testing.T) {
 	}, fs)
 	require.Equal(t, 1, len(mp.fees))
 	require.Equal(t, utilityBalanceAndFees{
-		balance: big.NewInt(fs.balance),
-		feeSum:  big.NewInt(tx2.NetworkFee),
+		balance: *uint256.NewInt(uint64(fs.balance)),
+		feeSum:  *uint256.NewInt(uint64(tx2.NetworkFee)),
 	}, mp.fees[sender0])
 
 	// there should be nothing left
diff --git a/pkg/core/native/native_neo.go b/pkg/core/native/native_neo.go
index 53604bca3..eb5291d87 100644
--- a/pkg/core/native/native_neo.go
+++ b/pkg/core/native/native_neo.go
@@ -90,6 +90,12 @@ const (
 var (
 	// prefixCommittee is a key used to store committee.
 	prefixCommittee = []byte{14}
+
+	bigCommitteeRewardRatio  = big.NewInt(committeeRewardRatio)
+	bigVoterRewardRatio      = big.NewInt(voterRewardRatio)
+	bigVoterRewardFactor     = big.NewInt(voterRewardFactor)
+	bigEffectiveVoterTurnout = big.NewInt(effectiveVoterTurnout)
+	big100                   = big.NewInt(100)
 )
 
 // makeValidatorKey creates a key from account script hash.
@@ -316,24 +322,26 @@ func (n *NEO) PostPersist(ic *interop.Context) error {
 	pubs := n.GetCommitteeMembers()
 	committeeSize := len(ic.Chain.GetConfig().StandbyCommittee)
 	index := int(ic.Block.Index) % committeeSize
-	committeeReward := new(big.Int).Mul(gas, big.NewInt(committeeRewardRatio))
-	n.GAS.mint(ic, pubs[index].GetScriptHash(), committeeReward.Div(committeeReward, big.NewInt(100)), false)
+	committeeReward := new(big.Int).Mul(gas, bigCommitteeRewardRatio)
+	n.GAS.mint(ic, pubs[index].GetScriptHash(), committeeReward.Div(committeeReward, big100), false)
 
 	if ShouldUpdateCommittee(ic.Block.Index, ic.Chain) {
-		var voterReward = big.NewInt(voterRewardRatio)
+		var voterReward = new(big.Int).Set(bigVoterRewardRatio)
 		voterReward.Mul(voterReward, gas)
 		voterReward.Mul(voterReward, big.NewInt(voterRewardFactor*int64(committeeSize)))
 		var validatorsCount = ic.Chain.GetConfig().ValidatorsCount
 		voterReward.Div(voterReward, big.NewInt(int64(committeeSize+validatorsCount)))
-		voterReward.Div(voterReward, big.NewInt(100))
+		voterReward.Div(voterReward, big100)
 
 		var cs = n.committee.Load().(keysWithVotes)
 		var key = make([]byte, 38)
 		for i := range cs {
 			if cs[i].Votes.Sign() > 0 {
-				tmp := big.NewInt(1)
+				var tmp = new(big.Int)
 				if i < validatorsCount {
-					tmp = big.NewInt(2)
+					tmp.Set(intTwo)
+				} else {
+					tmp.Set(intOne)
 				}
 				tmp.Mul(tmp, voterReward)
 				tmp.Div(tmp, cs[i].Votes)
@@ -633,7 +641,7 @@ func (n *NEO) calculateBonus(d dao.DAO, vote *keys.PublicKey, value *big.Int, st
 	var reward = n.getGASPerVote(d, key, start, end)
 	var tmp = new(big.Int).Sub(&reward[1], &reward[0])
 	tmp.Mul(tmp, value)
-	tmp.Div(tmp, big.NewInt(voterRewardFactor))
+	tmp.Div(tmp, bigVoterRewardFactor)
 	tmp.Add(tmp, r)
 	return tmp, nil
 }
@@ -982,7 +990,7 @@ func (n *NEO) computeCommitteeMembers(bc blockchainer.Blockchainer, d dao.DAO) (
 	}
 	votersCount := bigint.FromBytes(si)
 	// votersCount / totalSupply must be >= 0.2
-	votersCount.Mul(votersCount, big.NewInt(effectiveVoterTurnout))
+	votersCount.Mul(votersCount, bigEffectiveVoterTurnout)
 	_, totalSupply := n.getTotalSupply(d)
 	voterTurnout := votersCount.Div(votersCount, totalSupply)
 
diff --git a/pkg/core/native/util.go b/pkg/core/native/util.go
index afb20728c..0fadf740d 100644
--- a/pkg/core/native/util.go
+++ b/pkg/core/native/util.go
@@ -13,6 +13,7 @@ import (
 )
 
 var intOne = big.NewInt(1)
+var intTwo = big.NewInt(2)
 
 func getConvertibleFromDAO(id int32, d dao.DAO, key []byte, conv stackitem.Convertible) error {
 	si := d.GetStorageItem(id, key)
diff --git a/pkg/core/storage/memcached_store.go b/pkg/core/storage/memcached_store.go
index 065c7303f..d9a6dcbbc 100644
--- a/pkg/core/storage/memcached_store.go
+++ b/pkg/core/storage/memcached_store.go
@@ -252,8 +252,8 @@ func (s *MemCachedStore) persist(isSync bool) (int, error) {
 	// unprotected while writes are handled by s proper.
 	var tempstore = &MemCachedStore{MemoryStore: MemoryStore{mem: s.mem, del: s.del}, ps: s.ps}
 	s.ps = tempstore
-	s.mem = make(map[string][]byte)
-	s.del = make(map[string]bool)
+	s.mem = make(map[string][]byte, len(s.mem))
+	s.del = make(map[string]bool, len(s.del))
 	if !isSync {
 		s.mut.Unlock()
 	}
diff --git a/pkg/crypto/keys/publickey.go b/pkg/crypto/keys/publickey.go
index f39a15b1d..ecbeee259 100644
--- a/pkg/crypto/keys/publickey.go
+++ b/pkg/crypto/keys/publickey.go
@@ -29,6 +29,9 @@ const SignatureLen = 64
 // PublicKeys is a list of public keys.
 type PublicKeys []*PublicKey
 
+var big0 = big.NewInt(0)
+var big3 = big.NewInt(3)
+
 func (keys PublicKeys) Len() int      { return len(keys) }
 func (keys PublicKeys) Swap(i, j int) { keys[i], keys[j] = keys[j], keys[i] }
 func (keys PublicKeys) Less(i, j int) bool {
@@ -189,12 +192,12 @@ func decodeCompressedY(x *big.Int, ylsb uint, curve elliptic.Curve) (*big.Int, e
 	var a *big.Int
 	switch curve.(type) {
 	case *btcec.KoblitzCurve:
-		a = big.NewInt(0)
+		a = big0
 	default:
-		a = big.NewInt(3)
+		a = big3
 	}
 	cp := curve.Params()
-	xCubed := new(big.Int).Exp(x, big.NewInt(3), cp.P)
+	xCubed := new(big.Int).Exp(x, big3, cp.P)
 	aX := new(big.Int).Mul(x, a)
 	aX.Mod(aX, cp.P)
 	ySquared := new(big.Int).Sub(xCubed, aX)
diff --git a/pkg/encoding/bigint/bigint.go b/pkg/encoding/bigint/bigint.go
index b2ab067b0..a6b80b70a 100644
--- a/pkg/encoding/bigint/bigint.go
+++ b/pkg/encoding/bigint/bigint.go
@@ -15,6 +15,8 @@ const (
 	wordSizeBytes = bits.UintSize / 8
 )
 
+var bigOne = big.NewInt(1)
+
 // FromBytesUnsigned converts data in little-endian format to an unsigned integer.
 func FromBytesUnsigned(data []byte) *big.Int {
 	bs := slice.CopyReverse(data)
@@ -70,7 +72,7 @@ func FromBytes(data []byte) *big.Int {
 		n.SetBits(ws)
 		n.Neg(n)
 
-		return n.Sub(n, big.NewInt(1))
+		return n.Sub(n, bigOne)
 	}
 
 	return n.SetBits(ws)
@@ -114,7 +116,7 @@ func ToPreallocatedBytes(n *big.Int, data []byte) []byte {
 	if sign == 1 {
 		ws = n.Bits()
 	} else {
-		n1 := new(big.Int).Add(n, big.NewInt(1))
+		n1 := new(big.Int).Add(n, bigOne)
 		if n1.Sign() == 0 { // n == -1
 			return append(data, 0xFF)
 		}
diff --git a/pkg/io/binaryWriter.go b/pkg/io/binaryWriter.go
index 5f234c1b4..dc563b149 100644
--- a/pkg/io/binaryWriter.go
+++ b/pkg/io/binaryWriter.go
@@ -143,7 +143,11 @@ func (w *BinWriter) WriteVarBytes(b []byte) {
 
 // WriteString writes a variable length string into the underlying io.Writer.
 func (w *BinWriter) WriteString(s string) {
-	w.WriteVarBytes([]byte(s))
+	w.WriteVarUint(uint64(len(s)))
+	if w.Err != nil {
+		return
+	}
+	_, w.Err = io.WriteString(w.w, s)
 }
 
 // Grow tries to increase underlying buffer capacity so that at least n bytes
diff --git a/pkg/vm/context.go b/pkg/vm/context.go
index 1eaba0ce0..3cbace4b7 100644
--- a/pkg/vm/context.go
+++ b/pkg/vm/context.go
@@ -32,9 +32,9 @@ type Context struct {
 	// Evaluation stack pointer.
 	estack *Stack
 
-	static    *Slot
-	local     *Slot
-	arguments *Slot
+	static    *slot
+	local     slot
+	arguments slot
 
 	// Exception context stack.
 	tryStack Stack
@@ -277,16 +277,19 @@ func (c *Context) DumpStaticSlot() string {
 
 // DumpLocalSlot returns json formatted representation of the given slot.
 func (c *Context) DumpLocalSlot() string {
-	return dumpSlot(c.local)
+	return dumpSlot(&c.local)
 }
 
 // DumpArgumentsSlot returns json formatted representation of the given slot.
 func (c *Context) DumpArgumentsSlot() string {
-	return dumpSlot(c.arguments)
+	return dumpSlot(&c.arguments)
 }
 
 // dumpSlot returns json formatted representation of the given slot.
-func dumpSlot(s *Slot) string {
+func dumpSlot(s *slot) string {
+	if s == nil || *s == nil {
+		return "[]"
+	}
 	b, _ := json.MarshalIndent(s, "", "    ")
 	return string(b)
 }
diff --git a/pkg/vm/json_test.go b/pkg/vm/json_test.go
index 5d7f6acf5..bd15eba66 100644
--- a/pkg/vm/json_test.go
+++ b/pkg/vm/json_test.go
@@ -239,8 +239,8 @@ func compareStacks(t *testing.T, expected []vmUTStackItem, actual *Stack) {
 	compareItemArrays(t, expected, actual.Len(), func(i int) stackitem.Item { return actual.Peek(i).Item() })
 }
 
-func compareSlots(t *testing.T, expected []vmUTStackItem, actual *Slot) {
-	if actual.storage == nil && len(expected) == 0 {
+func compareSlots(t *testing.T, expected []vmUTStackItem, actual *slot) {
+	if (actual == nil || *actual == nil) && len(expected) == 0 {
 		return
 	}
 	require.NotNil(t, actual)
diff --git a/pkg/vm/opcodebench_test.go b/pkg/vm/opcodebench_test.go
index 1657d4151..465a9943e 100644
--- a/pkg/vm/opcodebench_test.go
+++ b/pkg/vm/opcodebench_test.go
@@ -59,8 +59,8 @@ func opParamSlotsPushVM(op opcode.Opcode, param []byte, sslot int, slotloc int,
 			v.Context().static.init(sslot)
 		}
 		if slotloc != 0 && slotarg != 0 {
-			v.Context().local = v.newSlot(slotloc)
-			v.Context().arguments = v.newSlot(slotarg)
+			v.Context().local.init(slotloc)
+			v.Context().arguments.init(slotarg)
 		}
 		for i := range items {
 			item, ok := items[i].(stackitem.Item)
diff --git a/pkg/vm/slot.go b/pkg/vm/slot.go
index 634891f18..132ee220c 100644
--- a/pkg/vm/slot.go
+++ b/pkg/vm/slot.go
@@ -6,75 +6,58 @@ import (
 	"github.com/nspcc-dev/neo-go/pkg/vm/stackitem"
 )
 
-// Slot is a fixed-size slice of stack items.
-type Slot struct {
-	storage []stackitem.Item
-	refs    *refCounter
-}
-
-// newSlot returns new slot with the provided reference counter.
-func newSlot(refs *refCounter) *Slot {
-	return &Slot{
-		refs: refs,
-	}
-}
+// slot is a fixed-size slice of stack items.
+type slot []stackitem.Item
 
 // init sets static slot size to n. It is intended to be used only by INITSSLOT.
-func (s *Slot) init(n int) {
-	if s.storage != nil {
+func (s *slot) init(n int) {
+	if *s != nil {
 		panic("already initialized")
 	}
-	s.storage = make([]stackitem.Item, n)
-}
-
-func (v *VM) newSlot(n int) *Slot {
-	s := newSlot(&v.refs)
-	s.init(n)
-	return s
+	*s = make([]stackitem.Item, n)
 }
 
 // Set sets i-th storage slot.
-func (s *Slot) Set(i int, item stackitem.Item) {
-	if s.storage[i] == item {
+func (s slot) Set(i int, item stackitem.Item, refs *refCounter) {
+	if s[i] == item {
 		return
 	}
-	old := s.storage[i]
-	s.storage[i] = item
+	old := s[i]
+	s[i] = item
 	if old != nil {
-		s.refs.Remove(old)
+		refs.Remove(old)
 	}
-	s.refs.Add(item)
+	refs.Add(item)
 }
 
 // Get returns item contained in i-th slot.
-func (s *Slot) Get(i int) stackitem.Item {
-	if item := s.storage[i]; item != nil {
+func (s slot) Get(i int) stackitem.Item {
+	if item := s[i]; item != nil {
 		return item
 	}
 	return stackitem.Null{}
 }
 
 // Clear removes all slot variables from reference counter.
-func (s *Slot) Clear() {
-	for _, item := range s.storage {
-		s.refs.Remove(item)
+func (s slot) Clear(refs *refCounter) {
+	for _, item := range s {
+		refs.Remove(item)
 	}
 }
 
 // Size returns slot size.
-func (s *Slot) Size() int {
-	if s.storage == nil {
+func (s slot) Size() int {
+	if s == nil {
 		panic("not initialized")
 	}
-	return len(s.storage)
+	return len(s)
 }
 
 // MarshalJSON implements JSON marshalling interface.
-func (s *Slot) MarshalJSON() ([]byte, error) {
-	items := s.storage
-	arr := make([]json.RawMessage, len(items))
-	for i := range items {
-		data, err := stackitem.ToJSONWithTypes(items[i])
+func (s slot) MarshalJSON() ([]byte, error) {
+	arr := make([]json.RawMessage, len(s))
+	for i := range s {
+		data, err := stackitem.ToJSONWithTypes(s[i])
 		if err == nil {
 			arr[i] = data
 		}
diff --git a/pkg/vm/slot_test.go b/pkg/vm/slot_test.go
index 434464476..212470a9f 100644
--- a/pkg/vm/slot_test.go
+++ b/pkg/vm/slot_test.go
@@ -9,8 +9,8 @@ import (
 )
 
 func TestSlot_Get(t *testing.T) {
-	s := newSlot(newRefCounter())
-	require.NotNil(t, s)
+	rc := newRefCounter()
+	var s slot
 	require.Panics(t, func() { s.Size() })
 
 	s.init(3)
@@ -20,6 +20,6 @@ func TestSlot_Get(t *testing.T) {
 	item := s.Get(2)
 	require.Equal(t, stackitem.Null{}, item)
 
-	s.Set(1, stackitem.NewBigInteger(big.NewInt(42)))
+	s.Set(1, stackitem.NewBigInteger(big.NewInt(42)), rc)
 	require.Equal(t, stackitem.NewBigInteger(big.NewInt(42)), s.Get(1))
 }
diff --git a/pkg/vm/stackitem/item.go b/pkg/vm/stackitem/item.go
index 14ed782e8..8fccd7ca2 100644
--- a/pkg/vm/stackitem/item.go
+++ b/pkg/vm/stackitem/item.go
@@ -1097,7 +1097,7 @@ func (i *Buffer) Len() int {
 // Values of Interop items are not deeply copied.
 // It does preserve duplicates only for non-primitive types.
 func DeepCopy(item Item) Item {
-	seen := make(map[Item]Item)
+	seen := make(map[Item]Item, typicalNumOfItems)
 	return deepCopy(item, seen)
 }
 
diff --git a/pkg/vm/stackitem/json.go b/pkg/vm/stackitem/json.go
index bb01076b0..9fd151d7a 100644
--- a/pkg/vm/stackitem/json.go
+++ b/pkg/vm/stackitem/json.go
@@ -42,7 +42,7 @@ var ErrTooDeep = errors.New("too deep")
 //   Array, Struct -> array
 //   Map -> map with keys as UTF-8 bytes
 func ToJSON(item Item) ([]byte, error) {
-	seen := make(map[Item]sliceNoPointer)
+	seen := make(map[Item]sliceNoPointer, typicalNumOfItems)
 	return toJSON(nil, seen, item)
 }
 
@@ -260,7 +260,7 @@ func (d *decoder) decodeMap() (*Map, error) {
 
 // ToJSONWithTypes serializes any stackitem to JSON in a lossless way.
 func ToJSONWithTypes(item Item) ([]byte, error) {
-	result, err := toJSONWithTypes(item, make(map[Item]bool))
+	result, err := toJSONWithTypes(item, make(map[Item]bool, typicalNumOfItems))
 	if err != nil {
 		return nil, err
 	}
diff --git a/pkg/vm/stackitem/serialization.go b/pkg/vm/stackitem/serialization.go
index bda4fbc80..50c5a5f2e 100644
--- a/pkg/vm/stackitem/serialization.go
+++ b/pkg/vm/stackitem/serialization.go
@@ -13,6 +13,12 @@ import (
 // (including itself).
 const MaxDeserialized = 2048
 
+// typicalNumOfItems is the number of items covering most serializaton needs.
+// It's a hint used for map creation, so it's not limiting anything, it's just
+// a microoptimization to avoid excessive reallocations. Most of the serialized
+// items are structs, so there is at least one of them.
+const typicalNumOfItems = 4
+
 // ErrRecursive is returned on attempts to serialize some recursive stack item
 // (like array including an item with reference to the same array).
 var ErrRecursive = errors.New("recursive item")
@@ -40,7 +46,7 @@ type deserContext struct {
 func Serialize(item Item) ([]byte, error) {
 	sc := serContext{
 		allowInvalid: false,
-		seen:         make(map[Item]sliceNoPointer),
+		seen:         make(map[Item]sliceNoPointer, typicalNumOfItems),
 	}
 	err := sc.serialize(item)
 	if err != nil {
@@ -69,7 +75,7 @@ func EncodeBinary(item Item, w *io.BinWriter) {
 func EncodeBinaryProtected(item Item, w *io.BinWriter) {
 	sc := serContext{
 		allowInvalid: true,
-		seen:         make(map[Item]sliceNoPointer),
+		seen:         make(map[Item]sliceNoPointer, typicalNumOfItems),
 	}
 	err := sc.serialize(item)
 	if err != nil {
@@ -79,6 +85,18 @@ func EncodeBinaryProtected(item Item, w *io.BinWriter) {
 	w.WriteBytes(sc.data)
 }
 
+func (w *serContext) writeArray(item Item, arr []Item, start int) error {
+	w.seen[item] = sliceNoPointer{}
+	w.appendVarUint(uint64(len(arr)))
+	for i := range arr {
+		if err := w.serialize(arr[i]); err != nil {
+			return err
+		}
+	}
+	w.seen[item] = sliceNoPointer{start, len(w.data)}
+	return nil
+}
+
 func (w *serContext) serialize(item Item) error {
 	if v, ok := w.seen[item]; ok {
 		if v.start == v.end {
@@ -121,28 +139,20 @@ func (w *serContext) serialize(item Item) error {
 		} else {
 			return fmt.Errorf("%w: Interop", ErrUnserializable)
 		}
-	case *Array, *Struct:
-		w.seen[item] = sliceNoPointer{}
-
-		_, isArray := t.(*Array)
-		if isArray {
-			w.data = append(w.data, byte(ArrayT))
-		} else {
-			w.data = append(w.data, byte(StructT))
+	case *Array:
+		w.data = append(w.data, byte(ArrayT))
+		if err := w.writeArray(item, t.value, start); err != nil {
+			return err
 		}
-
-		arr := t.Value().([]Item)
-		w.appendVarUint(uint64(len(arr)))
-		for i := range arr {
-			if err := w.serialize(arr[i]); err != nil {
-				return err
-			}
+	case *Struct:
+		w.data = append(w.data, byte(StructT))
+		if err := w.writeArray(item, t.value, start); err != nil {
+			return err
 		}
-		w.seen[item] = sliceNoPointer{start, len(w.data)}
 	case *Map:
 		w.seen[item] = sliceNoPointer{}
 
-		elems := t.Value().([]MapElement)
+		elems := t.value
 		w.data = append(w.data, byte(MapT))
 		w.appendVarUint(uint64(len(elems)))
 		for i := range elems {
diff --git a/pkg/vm/vm.go b/pkg/vm/vm.go
index 960b0e4f7..33859b91c 100644
--- a/pkg/vm/vm.go
+++ b/pkg/vm/vm.go
@@ -90,6 +90,8 @@ type VM struct {
 	invTree *InvocationTree
 }
 
+var bigOne = big.NewInt(1)
+
 // New returns a new VM object ready to load AVM bytecode scripts.
 func New() *VM {
 	return NewWithTrigger(trigger.Application)
@@ -105,6 +107,7 @@ func NewWithTrigger(t trigger.Type) *VM {
 	}
 
 	initStack(&vm.istack, "invocation", nil)
+	vm.istack.elems = make([]Element, 0, 8) // Most of invocations use one-two contracts, but they're likely to have internal calls.
 	vm.estack = newStack("evaluation", &vm.refs)
 	return vm
 }
@@ -310,13 +313,15 @@ func (v *VM) LoadNEFMethod(exe *nef.File, caller util.Uint160, hash util.Uint160
 // It should be used for calling from native contracts.
 func (v *VM) loadScriptWithCallingHash(b []byte, exe *nef.File, caller util.Uint160,
 	hash util.Uint160, f callflag.CallFlag, rvcount int, offset int) {
+	var sl slot
+
 	v.checkInvocationStackSize()
 	ctx := NewContextWithParams(b, rvcount, offset)
 	v.estack = newStack("evaluation", &v.refs)
 	ctx.estack = v.estack
 	initStack(&ctx.tryStack, "exception", nil)
 	ctx.callFlag = f
-	ctx.static = newSlot(&v.refs)
+	ctx.static = &sl
 	ctx.scriptHash = hash
 	ctx.callingScriptHash = caller
 	ctx.NEF = exe
@@ -615,13 +620,13 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 			panic("zero argument")
 		}
 		if parameter[0] > 0 {
-			ctx.local = v.newSlot(int(parameter[0]))
+			ctx.local.init(int(parameter[0]))
 		}
 		if parameter[1] > 0 {
 			sz := int(parameter[1])
-			ctx.arguments = v.newSlot(sz)
+			ctx.arguments.init(sz)
 			for i := 0; i < sz; i++ {
-				ctx.arguments.Set(i, v.estack.Pop().Item())
+				ctx.arguments.Set(i, v.estack.Pop().Item(), &v.refs)
 			}
 		}
 
@@ -635,11 +640,11 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 	case opcode.STSFLD0, opcode.STSFLD1, opcode.STSFLD2, opcode.STSFLD3, opcode.STSFLD4, opcode.STSFLD5, opcode.STSFLD6:
 		item := v.estack.Pop().Item()
-		ctx.static.Set(int(op-opcode.STSFLD0), item)
+		ctx.static.Set(int(op-opcode.STSFLD0), item, &v.refs)
 
 	case opcode.STSFLD:
 		item := v.estack.Pop().Item()
-		ctx.static.Set(int(parameter[0]), item)
+		ctx.static.Set(int(parameter[0]), item, &v.refs)
 
 	case opcode.LDLOC0, opcode.LDLOC1, opcode.LDLOC2, opcode.LDLOC3, opcode.LDLOC4, opcode.LDLOC5, opcode.LDLOC6:
 		item := ctx.local.Get(int(op - opcode.LDLOC0))
@@ -651,11 +656,11 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 	case opcode.STLOC0, opcode.STLOC1, opcode.STLOC2, opcode.STLOC3, opcode.STLOC4, opcode.STLOC5, opcode.STLOC6:
 		item := v.estack.Pop().Item()
-		ctx.local.Set(int(op-opcode.STLOC0), item)
+		ctx.local.Set(int(op-opcode.STLOC0), item, &v.refs)
 
 	case opcode.STLOC:
 		item := v.estack.Pop().Item()
-		ctx.local.Set(int(parameter[0]), item)
+		ctx.local.Set(int(parameter[0]), item, &v.refs)
 
 	case opcode.LDARG0, opcode.LDARG1, opcode.LDARG2, opcode.LDARG3, opcode.LDARG4, opcode.LDARG5, opcode.LDARG6:
 		item := ctx.arguments.Get(int(op - opcode.LDARG0))
@@ -667,11 +672,11 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 	case opcode.STARG0, opcode.STARG1, opcode.STARG2, opcode.STARG3, opcode.STARG4, opcode.STARG5, opcode.STARG6:
 		item := v.estack.Pop().Item()
-		ctx.arguments.Set(int(op-opcode.STARG0), item)
+		ctx.arguments.Set(int(op-opcode.STARG0), item, &v.refs)
 
 	case opcode.STARG:
 		item := v.estack.Pop().Item()
-		ctx.arguments.Set(int(parameter[0]), item)
+		ctx.arguments.Set(int(parameter[0]), item, &v.refs)
 
 	case opcode.NEWBUFFER:
 		n := toInt(v.estack.Pop().BigInt())
@@ -887,12 +892,12 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 	case opcode.INC:
 		x := v.estack.Pop().BigInt()
-		a := new(big.Int).Add(x, big.NewInt(1))
+		a := new(big.Int).Add(x, bigOne)
 		v.estack.PushItem(stackitem.NewBigInteger(a))
 
 	case opcode.DEC:
 		x := v.estack.Pop().BigInt()
-		a := new(big.Int).Sub(x, big.NewInt(1))
+		a := new(big.Int).Sub(x, bigOne)
 		v.estack.PushItem(stackitem.NewBigInteger(a))
 
 	case opcode.ADD:
@@ -1527,14 +1532,14 @@ func (v *VM) execute(ctx *Context, op opcode.Opcode, parameter []byte) (err erro
 
 func (v *VM) unloadContext(ctx *Context) {
 	if ctx.local != nil {
-		ctx.local.Clear()
+		ctx.local.Clear(&v.refs)
 	}
 	if ctx.arguments != nil {
-		ctx.arguments.Clear()
+		ctx.arguments.Clear(&v.refs)
 	}
 	currCtx := v.Context()
 	if ctx.static != nil && currCtx != nil && ctx.static != currCtx.static {
-		ctx.static.Clear()
+		ctx.static.Clear(&v.refs)
 	}
 }