diff --git a/Cargo.lock b/Cargo.lock
index be5f3bc..c7e2204 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -319,6 +319,7 @@ dependencies = [
  "jobslot",
  "num-bigint",
  "num-traits",
+ "once_cell",
  "ordered-float",
  "petgraph",
  "serde",
@@ -521,9 +522,9 @@ dependencies = [
 
 [[package]]
 name = "once_cell"
-version = "1.19.0"
+version = "1.21.3"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "3fdb12b2476b595f9358c5161aa467c2438859caa136dec86c26fdd2efe17b92"
+checksum = "42f5e15c9953c5e4ccceeb2e7382a716482c34515315f7b03532b8b4e8393d2d"
 
 [[package]]
 name = "ordered-float"
diff --git a/Cargo.toml b/Cargo.toml
index 2380ea7..6559e2a 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -30,6 +30,7 @@ indexmap = { version = "2.5.0", features = ["serde"] }
 jobslot = "0.2.23"
 num-bigint = "0.4.6"
 num-traits = "0.2.16"
+once_cell = "1.21.3"
 ordered-float = { version = "5.1.0", features = ["serde"] }
 petgraph = "0.8.1"
 prettyplease = "0.2.20"
diff --git a/crates/fayalite/Cargo.toml b/crates/fayalite/Cargo.toml
index fdf1c87..61ee5c7 100644
--- a/crates/fayalite/Cargo.toml
+++ b/crates/fayalite/Cargo.toml
@@ -26,6 +26,7 @@ hashbrown.workspace = true
 jobslot.workspace = true
 num-bigint.workspace = true
 num-traits.workspace = true
+once_cell.workspace = true
 ordered-float.workspace = true
 petgraph.workspace = true
 serde_json.workspace = true
diff --git a/crates/fayalite/src/int.rs b/crates/fayalite/src/int.rs
index 2d1f6d2..c461306 100644
--- a/crates/fayalite/src/int.rs
+++ b/crates/fayalite/src/int.rs
@@ -10,7 +10,7 @@ use crate::{
         value_category::ValueCategoryValue,
     },
     hdl,
-    intern::{Intern, Interned, Memoize},
+    intern::{Intern, Interned, Memoize, OnceInterned},
     sim::value::{SimValue, ToSimValueWithType},
     source_location::SourceLocation,
     ty::{
@@ -65,14 +65,21 @@ pub type DynSize = ConstUsize<DYN_SIZE>;
 
 trait KnownSizeBaseSealed {}
 
-impl<const N: usize> KnownSizeBaseSealed for [(); N] {}
+impl<const N: usize> KnownSizeBaseSealed for ConstUsize<N> {}
 
 #[expect(private_bounds)]
-pub trait KnownSizeBase: KnownSizeBaseSealed {}
+pub trait KnownSizeBase: KnownSizeBaseSealed + GetInternedIntCaches {}
 
 macro_rules! impl_known_size_base {
     ($($size:literal),* $(,)?) => {
-        $(impl KnownSizeBase for [(); $size] {})*
+        $(impl KnownSizeBase for ConstUsize<$size> {})*
+        $(impl GetInternedIntCaches for ConstUsize<$size> {
+            #[inline(always)]
+            fn get_interned_int_caches() -> &'static InternedIntCaches<Self> {
+                static CACHES: InternedIntCaches<ConstUsize<$size>> = InternedIntCaches::new();
+                &CACHES
+            }
+        })*
     };
 }
 
@@ -113,12 +120,34 @@ impl_known_size_base! {
     0x200,
 }
 
+trait GetInternedIntCaches {
+    fn get_interned_int_caches() -> &'static InternedIntCaches<Self>
+    where
+        Self: KnownSize;
+}
+
+struct InternedIntCaches<Width: KnownSize> {
+    uint: OnceInterned<UIntType<Width>>,
+    sint: OnceInterned<SIntType<Width>>,
+}
+
+impl<Width: KnownSize> InternedIntCaches<Width> {
+    const fn new() -> Self {
+        Self {
+            uint: OnceInterned::new(),
+            sint: OnceInterned::new(),
+        }
+    }
+}
+
+#[expect(private_bounds)]
 pub trait KnownSize:
     GenericConstUsize
     + sealed::SizeTypeSealed
     + sealed::SizeSealed
     + Default
     + FillInDefaultedGenerics<Type = Self>
+    + GetInternedIntCaches
 {
     const SIZE: Self;
     type ArrayMatch<Element: Type>: AsRef<[Expr<Element>]>
@@ -148,7 +177,7 @@ pub trait KnownSize:
 
 impl<const N: usize> KnownSize for ConstUsize<N>
 where
-    [(); N]: KnownSizeBase,
+    ConstUsize<N>: KnownSizeBase,
 {
     const SIZE: Self = Self;
     type ArrayMatch<Element: Type> = [Expr<Element>; N];
@@ -221,6 +250,10 @@ pub trait Size:
     fn from_usize(v: usize) -> Self::SizeType {
         Self::try_from_usize(v).expect("wrong size")
     }
+    #[doc(hidden)]
+    fn interned_uint(size_type: Self::SizeType) -> Interned<UIntType<Self>>;
+    #[doc(hidden)]
+    fn interned_sint(size_type: Self::SizeType) -> Interned<SIntType<Self>>;
 }
 
 impl sealed::SizeTypeSealed for usize {}
@@ -229,6 +262,8 @@ impl SizeType for usize {
     type Size = DynSize;
 }
 
+const MAX_CACHED_INT_WIDTH: usize = 1 << 10;
+
 impl Size for DynSize {
     type ArrayMatch<Element: Type> = Box<[Expr<Element>]>;
     type ArraySimValue<Element: Type> = Box<[SimValue<Element>]>;
@@ -242,6 +277,36 @@ impl Size for DynSize {
     fn try_from_usize(v: usize) -> Option<Self::SizeType> {
         Some(v)
     }
+
+    #[doc(hidden)]
+    fn interned_uint(size_type: Self::SizeType) -> Interned<UIntType<Self>> {
+        static CACHED: [OnceInterned<UInt>; MAX_CACHED_INT_WIDTH] =
+            [const { OnceInterned::new() }; _];
+        #[cold]
+        fn intern_cold(width: usize) -> Interned<UInt> {
+            Intern::intern_sized(UInt::new(width))
+        }
+        if let Some(cached) = CACHED.get(size_type) {
+            cached.get_or_init(|| intern_cold(size_type))
+        } else {
+            intern_cold(size_type)
+        }
+    }
+
+    #[doc(hidden)]
+    fn interned_sint(size_type: Self::SizeType) -> Interned<SIntType<Self>> {
+        static CACHED: [OnceInterned<SInt>; MAX_CACHED_INT_WIDTH] =
+            [const { OnceInterned::new() }; _];
+        #[cold]
+        fn intern_cold(width: usize) -> Interned<SInt> {
+            Intern::intern_sized(SInt::new(width))
+        }
+        if let Some(cached) = CACHED.get(size_type) {
+            cached.get_or_init(|| intern_cold(size_type))
+        } else {
+            intern_cold(size_type)
+        }
+    }
 }
 
 impl<const VALUE: usize> sealed::SizeSealed for ConstUsize<VALUE> {}
@@ -267,6 +332,20 @@ impl<T: KnownSize> Size for T {
     fn try_from_usize(v: usize) -> Option<Self::SizeType> {
         if v == T::VALUE { Some(T::SIZE) } else { None }
     }
+
+    #[doc(hidden)]
+    fn interned_uint(_size_type: Self::SizeType) -> Interned<UIntType<Self>> {
+        T::get_interned_int_caches()
+            .uint
+            .get_or_init(|| UIntType::new_static().intern_sized())
+    }
+
+    #[doc(hidden)]
+    fn interned_sint(_size_type: Self::SizeType) -> Interned<SIntType<Self>> {
+        T::get_interned_int_caches()
+            .sint
+            .get_or_init(|| SIntType::new_static().intern_sized())
+    }
 }
 
 #[derive(Clone, PartialEq, Eq, Debug)]
@@ -586,7 +665,7 @@ macro_rules! impl_valueless_op_forward {
 }
 
 macro_rules! impl_int {
-    ($pretty_name:ident, $name:ident, $generic_name:ident, $value:ident, $SIGNED:literal) => {
+    ($pretty_name:ident, $name:ident, $generic_name:ident, $value:ident, $SIGNED:literal, $interned_int:ident) => {
         #[derive(Copy, Clone, PartialEq, Eq, Hash)]
         #[repr(transparent)]
         pub struct $name<Width: Size = DynSize> {
@@ -1003,7 +1082,7 @@ macro_rules! impl_int {
             type Output = $name<Width::Size>;
 
             fn index(&self, width: Width) -> &Self::Output {
-                Interned::into_inner(Intern::intern_sized($name::new(width)))
+                Interned::into_inner(Width::Size::$interned_int(width))
             }
         }
 
@@ -1184,8 +1263,22 @@ macro_rules! impl_int {
     };
 }
 
-impl_int!(UInt, UIntType, UIntWithoutGenerics, UIntValue, false);
-impl_int!(SInt, SIntType, SIntWithoutGenerics, SIntValue, true);
+impl_int!(
+    UInt,
+    UIntType,
+    UIntWithoutGenerics,
+    UIntValue,
+    false,
+    interned_uint
+);
+impl_int!(
+    SInt,
+    SIntType,
+    SIntWithoutGenerics,
+    SIntValue,
+    true,
+    interned_sint
+);
 
 impl UInt {
     /// gets the smallest `UInt` that fits `v` losslessly
diff --git a/crates/fayalite/src/intern.rs b/crates/fayalite/src/intern.rs
index b68140b..9ffd251 100644
--- a/crates/fayalite/src/intern.rs
+++ b/crates/fayalite/src/intern.rs
@@ -4,6 +4,7 @@
 use crate::{intern::type_map::TypeIdMap, util::DefaultBuildHasher};
 use bitvec::{ptr::BitPtr, slice::BitSlice, vec::BitVec};
 use hashbrown::HashTable;
+use once_cell::race::OnceRef;
 use serde::{Deserialize, Serialize};
 use std::{
     any::{Any, TypeId},
@@ -16,9 +17,10 @@ use std::{
     marker::PhantomData,
     ops::Deref,
     path::{Path, PathBuf},
-    sync::{Mutex, RwLock},
+    sync::RwLock,
 };
 
+mod interner;
 mod type_map;
 
 pub trait LazyInternedTrait<T: ?Sized + Send + Sync + 'static>: Send + Sync + Any {
@@ -593,71 +595,6 @@ impl<T: ?Sized + 'static + Send + Sync + ToOwned> From<Interned<T>> for Cow<'_,
     }
 }
 
-struct InternerState<T: ?Sized + 'static + Send + Sync> {
-    table: HashTable<&'static T>,
-    hasher: DefaultBuildHasher,
-}
-
-pub struct Interner<T: ?Sized + 'static + Send + Sync> {
-    state: Mutex<InternerState<T>>,
-}
-
-impl<T: ?Sized + 'static + Send + Sync> Interner<T> {
-    fn get() -> &'static Interner<T> {
-        static TYPE_ID_MAP: TypeIdMap = TypeIdMap::new();
-        TYPE_ID_MAP.get_or_insert_default()
-    }
-}
-
-impl<T: ?Sized + 'static + Send + Sync> Default for Interner<T> {
-    fn default() -> Self {
-        Self {
-            state: Mutex::new(InternerState {
-                table: HashTable::new(),
-                hasher: Default::default(),
-            }),
-        }
-    }
-}
-
-impl<T: ?Sized + 'static + Send + Sync + Hash + Eq + ToOwned> Interner<T> {
-    fn intern<F: FnOnce(Cow<'_, T>) -> &'static T>(
-        &self,
-        alloc: F,
-        value: Cow<'_, T>,
-    ) -> Interned<T> {
-        let mut state = self.state.lock().unwrap();
-        let InternerState { table, hasher } = &mut *state;
-        let inner = *table
-            .entry(
-                hasher.hash_one(&*value),
-                |k| **k == *value,
-                |k| hasher.hash_one(&**k),
-            )
-            .or_insert_with(|| alloc(value))
-            .get();
-        Interned { inner }
-    }
-}
-
-impl<T: Clone + 'static + Send + Sync + Hash + Eq> Interner<T> {
-    fn intern_sized(&self, value: Cow<'_, T>) -> Interned<T> {
-        self.intern(|value| Box::leak(Box::new(value.into_owned())), value)
-    }
-}
-
-impl<T: Clone + 'static + Send + Sync + Hash + Eq> Interner<[T]> {
-    fn intern_slice(&self, value: Cow<'_, [T]>) -> Interned<[T]> {
-        self.intern(|value| value.into_owned().leak(), value)
-    }
-}
-
-impl Interner<BitSlice> {
-    fn intern_bit_slice(&self, value: Cow<'_, BitSlice>) -> Interned<BitSlice> {
-        self.intern(|value| value.into_owned().leak(), value)
-    }
-}
-
 pub struct Interned<T: ?Sized + 'static + Send + Sync> {
     inner: &'static T,
 }
@@ -977,7 +914,7 @@ impl<T: Clone + Send + Sync + 'static + Hash + Eq> Intern for T {
     where
         Self: ToOwned,
     {
-        Interner::get().intern_sized(this)
+        interner::Interner::get().intern_sized(this)
     }
 }
 
@@ -997,7 +934,7 @@ impl<T: Clone + Send + Sync + 'static + Hash + Eq> Intern for [T] {
     where
         Self: ToOwned,
     {
-        Interner::get().intern_slice(this)
+        interner::Interner::get().intern_slice(this)
     }
 }
 
@@ -1017,7 +954,7 @@ impl Intern for BitSlice {
     where
         Self: ToOwned,
     {
-        Interner::get().intern_bit_slice(this)
+        interner::Interner::get().intern_bit_slice(this)
     }
 }
 
@@ -1035,10 +972,17 @@ pub trait MemoizeGeneric: 'static + Send + Sync + Hash + Eq + Copy {
     fn inner(self, input: Self::InputRef<'_>) -> Self::Output;
     fn get_cow(self, input: Self::InputCow<'_>) -> Self::Output {
         static TYPE_ID_MAP: TypeIdMap = TypeIdMap::new();
+        thread_local! {
+            static TYPE_ID_MAP_CACHE: TypeIdMap = const { TypeIdMap::new() };
+        }
         let map: &RwLock<(
             DefaultBuildHasher,
             HashTable<(Self, Self::InputOwned, Self::Output)>,
-        )> = TYPE_ID_MAP.get_or_insert_default();
+        )> = TYPE_ID_MAP_CACHE.with(|cache| {
+            cache.get_or_insert_with(|| {
+                TYPE_ID_MAP.get_or_insert_with(|| Box::leak(Default::default()))
+            })
+        });
         fn hash_eq_key<'a, 'b, T: MemoizeGeneric>(
             this: &'a T,
             input: T::InputRef<'b>,
@@ -1140,3 +1084,35 @@ pub trait Memoize: 'static + Send + Sync + Hash + Eq + Copy {
         self.get_cow(Cow::Borrowed(input))
     }
 }
+
+/// like `once_cell::race::OnceBox` but for `Interned<T>` instead of `Box<T>`
+pub struct OnceInterned<T: 'static + Send + Sync>(OnceRef<'static, T>);
+
+impl<T: 'static + Send + Sync + fmt::Debug> fmt::Debug for OnceInterned<T> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.debug_tuple("OnceInterned").field(&self.get()).finish()
+    }
+}
+
+impl<T: 'static + Send + Sync> Default for OnceInterned<T> {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+impl<T: 'static + Send + Sync> OnceInterned<T> {
+    pub const fn new() -> Self {
+        Self(OnceRef::new())
+    }
+    pub fn set(&self, v: Interned<T>) -> Result<(), ()> {
+        self.0.set(v.inner)
+    }
+    pub fn get(&self) -> Option<Interned<T>> {
+        self.0.get().map(|inner| Interned { inner })
+    }
+    pub fn get_or_init<F: FnOnce() -> Interned<T>>(&self, f: F) -> Interned<T> {
+        Interned {
+            inner: self.0.get_or_init(|| f().inner),
+        }
+    }
+}
diff --git a/crates/fayalite/src/intern/interner.rs b/crates/fayalite/src/intern/interner.rs
new file mode 100644
index 0000000..4e35636
--- /dev/null
+++ b/crates/fayalite/src/intern/interner.rs
@@ -0,0 +1,117 @@
+// SPDX-License-Identifier: LGPL-3.0-or-later
+// See Notices.txt for copyright information
+
+use crate::{
+    intern::{Interned, type_map::TypeIdMap},
+    util::DefaultBuildHasher,
+};
+use bitvec::slice::BitSlice;
+use hashbrown::HashTable;
+use std::{
+    borrow::Cow,
+    hash::{BuildHasher, Hash},
+    sync::RwLock,
+};
+
+struct InternerShard<T: ?Sized + 'static + Send + Sync> {
+    table: HashTable<&'static T>,
+}
+
+const LOG2_SHARD_COUNT: u32 = 6;
+
+fn shard_index_from_hash(hash: u64) -> usize {
+    // number of bits used for hashbrown's Tag
+    const HASH_BROWN_TAG_BITS: u32 = 7;
+    // try to extract bits of the hash that hashbrown isn't using,
+    // while accounting for some hash functions only returning `usize` bits.
+    const SHARD_INDEX_START: u32 = usize::BITS
+        .saturating_sub(HASH_BROWN_TAG_BITS)
+        .saturating_sub(LOG2_SHARD_COUNT);
+    let mut shard_index = hash >> SHARD_INDEX_START;
+    shard_index %= 1 << LOG2_SHARD_COUNT;
+    shard_index as usize
+}
+
+pub(crate) struct Interner<T: ?Sized + 'static + Send + Sync> {
+    shards: [RwLock<InternerShard<T>>; 1 << LOG2_SHARD_COUNT],
+    hasher: DefaultBuildHasher,
+}
+
+impl<T: ?Sized + 'static + Send + Sync> Interner<T> {
+    pub(crate) fn get() -> &'static Interner<T> {
+        static TYPE_ID_MAP: TypeIdMap = TypeIdMap::new();
+        thread_local! {
+            static TYPE_ID_MAP_CACHE: TypeIdMap = const { TypeIdMap::new() };
+        }
+        TYPE_ID_MAP_CACHE.with(|cache| {
+            cache.get_or_insert_with(|| {
+                TYPE_ID_MAP.get_or_insert_with(|| Box::leak(Default::default()))
+            })
+        })
+    }
+}
+
+impl<T: ?Sized + 'static + Send + Sync> Default for Interner<T> {
+    fn default() -> Self {
+        Self {
+            shards: [const {
+                RwLock::new(InternerShard {
+                    table: HashTable::new(),
+                })
+            }; _],
+            hasher: Default::default(),
+        }
+    }
+}
+
+impl<T: ?Sized + 'static + Send + Sync + Hash + Eq + ToOwned> Interner<T> {
+    fn intern<F: FnOnce(Cow<'_, T>) -> &'static T>(
+        &self,
+        alloc: F,
+        value: Cow<'_, T>,
+    ) -> Interned<T> {
+        let hash = self.hasher.hash_one(&*value);
+        let shard_index = shard_index_from_hash(hash);
+        let shard = &self.shards[shard_index];
+        let shard_read = shard.read().unwrap();
+        let Some(&inner) = shard_read.table.find(hash, |k| **k == *value) else {
+            drop(shard_read);
+            return self.intern_cold(alloc, value, hash, shard);
+        };
+        Interned { inner }
+    }
+    #[cold]
+    fn intern_cold<F: FnOnce(Cow<'_, T>) -> &'static T>(
+        &self,
+        alloc: F,
+        value: Cow<'_, T>,
+        hash: u64,
+        shard: &RwLock<InternerShard<T>>,
+    ) -> Interned<T> {
+        let mut shard = shard.write().unwrap();
+        let inner = *shard
+            .table
+            .entry(hash, |k| **k == *value, |k| self.hasher.hash_one(&**k))
+            .or_insert_with(|| alloc(value))
+            .get();
+        Interned { inner }
+    }
+}
+
+impl<T: Clone + 'static + Send + Sync + Hash + Eq> Interner<T> {
+    pub(crate) fn intern_sized(&self, value: Cow<'_, T>) -> Interned<T> {
+        self.intern(|value| Box::leak(Box::new(value.into_owned())), value)
+    }
+}
+
+impl<T: Clone + 'static + Send + Sync + Hash + Eq> Interner<[T]> {
+    pub(crate) fn intern_slice(&self, value: Cow<'_, [T]>) -> Interned<[T]> {
+        self.intern(|value| value.into_owned().leak(), value)
+    }
+}
+
+impl Interner<BitSlice> {
+    pub(crate) fn intern_bit_slice(&self, value: Cow<'_, BitSlice>) -> Interned<BitSlice> {
+        self.intern(|value| value.into_owned().leak(), value)
+    }
+}
diff --git a/crates/fayalite/src/intern/type_map.rs b/crates/fayalite/src/intern/type_map.rs
index 945116b..03b68e3 100644
--- a/crates/fayalite/src/intern/type_map.rs
+++ b/crates/fayalite/src/intern/type_map.rs
@@ -87,20 +87,23 @@ impl TypeIdMap {
     fn insert_slow(
         &self,
         type_id: TypeId,
-        make: fn() -> Box<dyn Any + Sync + Send>,
+        make: impl FnOnce() -> &'static (dyn Any + Sync + Send),
     ) -> &'static (dyn Any + Sync + Send) {
-        let value = Box::leak(make());
+        let value = make();
         let mut write_guard = self.0.write().unwrap();
         *write_guard.entry(type_id).or_insert(value)
     }
-    pub(crate) fn get_or_insert_default<T: Sized + Any + Send + Sync + Default>(&self) -> &T {
+    pub(crate) fn get_or_insert_with<T: Sized + Any + Send + Sync>(
+        &self,
+        make: impl FnOnce() -> &'static T,
+    ) -> &'static T {
         let type_id = TypeId::of::<T>();
         let read_guard = self.0.read().unwrap();
         let retval = read_guard.get(&type_id).map(|v| *v);
         drop(read_guard);
         let retval = match retval {
             Some(retval) => retval,
-            None => self.insert_slow(type_id, move || Box::new(T::default())),
+            None => self.insert_slow(type_id, move || make()),
         };
         retval.downcast_ref().expect("known to have correct TypeId")
     }