diff --git a/include/artic/ast.h b/include/artic/ast.h
index 401450d8..6f175501 100644
--- a/include/artic/ast.h
+++ b/include/artic/ast.h
@@ -1506,6 +1506,32 @@ struct TypeDecl : public NamedDecl {
     void print(Printer&) const override;
 };
 
+struct ExtTypeDecl : public NamedDecl {
+    Ptr<TypeParamList> type_params;
+    std::string type_name;
+    std::vector<std::variant<Ptr<Type>, Ptr<Expr>>> args_;
+    std::vector<const artic::Type*> args_types_;
+
+    ExtTypeDecl(
+        const Loc& loc,
+        Identifier&& id,
+        std::string&& type_name,
+        Ptr<TypeParamList>&& type_params,
+        std::vector<std::variant<Ptr<Type>, Ptr<Expr>>>&& args)
+        : NamedDecl(loc, std::move(id))
+        , type_name(type_name)
+        , type_params(std::move(type_params))
+        , args_(std::move(args)) {
+    }
+
+    const thorin::Def* emit(Emitter&) const override;
+    const artic::Type* infer(TypeChecker&) override;
+    void bind_head(NameBinder&) override;
+    void bind(NameBinder&) override;
+    void resolve_summons(Summoner&) override {};
+    void print(Printer&) const override;
+};
+
 /// Module definition.
 struct ModDecl : public NamedDecl {
     PtrVector<Decl> decls;
diff --git a/include/artic/parser.h b/include/artic/parser.h
index 8d5c0de1..bdf4d565 100644
--- a/include/artic/parser.h
+++ b/include/artic/parser.h
@@ -34,6 +34,7 @@ class Parser : public Logger {
     Ptr<ast::ImplicitDecl>  parse_implicit_decl();
     Ptr<ast::StaticDecl>    parse_static_decl();
     Ptr<ast::TypeDecl>      parse_type_decl();
+    Ptr<ast::ExtTypeDecl>   parse_ext_type_decl();
     Ptr<ast::TypeParam>     parse_type_param();
     Ptr<ast::TypeParamList> parse_type_params();
     Ptr<ast::ModDecl>       parse_mod_decl();
diff --git a/include/artic/token.h b/include/artic/token.h
index a641430b..81ff9cfa 100644
--- a/include/artic/token.h
+++ b/include/artic/token.h
@@ -30,6 +30,7 @@ namespace artic {
     f(Struct, "struct") \
     f(Enum, "enum") \
     f(Type, "type") \
+    f(TypeExt, "type_ext") \
     f(Static, "static") \
     f(Implicit, "implicit") \
     f(Summon, "summon") \
diff --git a/include/artic/types.h b/include/artic/types.h
index 3a6955ad..c5e82e92 100644
--- a/include/artic/types.h
+++ b/include/artic/types.h
@@ -582,6 +582,22 @@ struct TypeAlias : public PolyTypeFromDecl<UserType, ast::TypeDecl> {
     friend class TypeTable;
 };
 
+struct ExtType : public PolyTypeFromDecl<UserType, ast::ExtTypeDecl> {
+    void print(Printer&) const override;
+
+private:
+    ExtType(TypeTable& type_table, const ast::ExtTypeDecl& decl)
+        : PolyTypeFromDecl(type_table, decl)
+    {}
+
+    using UserType::convert;
+    const thorin::Type* convert(Emitter&, const Type*) const override;
+
+    std::string stringify(Emitter&) const override;
+
+    friend class TypeTable;
+};
+
 /// An application of a complex type with polymorphic parameters.
 struct TypeApp : public Type {
     const UserType* applied;
@@ -684,6 +700,7 @@ class TypeTable {
     const EnumType*          enum_type(const ast::EnumDecl&);
     const ModType*           mod_type(const ast::ModDecl&);
     const TypeAlias*         type_alias(const ast::TypeDecl&);
+    const ExtType*           ext_type(const ast::ExtTypeDecl&);
 
     /// Creates a type application for structures/enumeration types,
     /// or returns the type alias expanded with the given type arguments.
diff --git a/src/bind.cpp b/src/bind.cpp
index 37c4a3f4..3bdc71f2 100644
--- a/src/bind.cpp
+++ b/src/bind.cpp
@@ -509,6 +509,10 @@ void TypeDecl::bind_head(NameBinder& binder) {
     binder.insert_symbol(*this);
 }
 
+void ExtTypeDecl::bind_head(NameBinder& binder) {
+    binder.insert_symbol(*this);
+}
+
 void TypeDecl::bind(NameBinder& binder) {
     binder.push_scope();
     if (type_params) binder.bind(*type_params);
@@ -516,6 +520,20 @@ void TypeDecl::bind(NameBinder& binder) {
     binder.pop_scope();
 }
 
+void ExtTypeDecl::bind(NameBinder& binder) {
+    binder.push_scope();
+    //if (type_params) binder.bind(*type_params);
+    for (auto& arg : args_) {
+        if (auto t = std::get_if<Ptr<Type>>(&arg))
+            binder.bind(**t);
+        else if (auto e = std::get_if<Ptr<Expr>>(&arg))
+            binder.bind(**e);
+        else
+            assert(false);
+    }
+    binder.pop_scope();
+}
+
 void ModDecl::bind_head(NameBinder& binder) {
     if (id.name != "")
         binder.insert_symbol(*this);
diff --git a/src/check.cpp b/src/check.cpp
index fa6f01f9..a0315a2d 100644
--- a/src/check.cpp
+++ b/src/check.cpp
@@ -83,7 +83,7 @@ const Type* TypeChecker::invalid_cast(const Loc& loc, const Type* type, const Ty
 
 const Type* TypeChecker::invalid_simd(const Loc& loc, const Type* elem_type) {
     if (should_report_error(elem_type))
-        error(loc, "expected primitive type for simd type component, but got '{}'", *elem_type);
+        error(loc, "expected primitive or pointer type for simd type component, but got '{}'", *elem_type);
     return type_table.type_error();
 }
 
@@ -489,7 +489,7 @@ const Type* TypeChecker::infer_array(
     if (elem_count == 0)
         return cannot_infer(loc, msg);
     auto elem_type = infer_elems();
-    if (is_simd && !elem_type->template isa<PrimType>())
+    if (is_simd && !(elem_type->template isa<PrimType>() || elem_type->template isa<PtrType>()))
         return invalid_simd(loc, elem_type);
     return type_table.sized_array_type(elem_type, elem_count, is_simd);
 }
@@ -509,7 +509,7 @@ const Type* TypeChecker::check_array(
     if (is_simd_type(array_type) != is_simd)
         return incompatible_type(loc, (is_simd ? "simd " : "non-simd ") + std::string(msg), expected);
     auto elem_type = array_type->elem;
-    if (is_simd && !elem_type->isa<PrimType>())
+    if (is_simd && !(elem_type->template isa<PrimType>() || elem_type->template isa<PtrType>()))
         return invalid_simd(loc, elem_type);
     check_elems(elem_type);
     if (auto sized_array_type = array_type->isa<artic::SizedArrayType>();
@@ -847,7 +847,7 @@ const artic::Type* TupleType::infer(TypeChecker& checker) {
 
 const artic::Type* SizedArrayType::infer(TypeChecker& checker) {
     auto elem_type = checker.infer(*elem);
-    if (is_simd && !elem_type->isa<artic::PrimType>())
+    if (is_simd && !(elem_type->template isa<artic::PrimType>() || elem_type->template isa<artic::PtrType>()))
         return checker.invalid_simd(loc, elem_type);
 
     if (std::holds_alternative<ast::Path>(size)) {
@@ -1022,7 +1022,7 @@ const artic::Type* ArrayExpr::check(TypeChecker& checker, const artic::Type* exp
 
 const artic::Type* RepeatArrayExpr::infer(TypeChecker& checker) {
     auto elem_type = checker.deref(elem);
-    if (is_simd && !elem_type->isa<artic::PrimType>())
+    if (is_simd && !(elem_type->template isa<artic::PrimType>() || elem_type->template isa<artic::PtrType>()))
         return checker.invalid_simd(loc, elem_type);
 
     if (std::holds_alternative<ast::Path>(size)) {
@@ -1816,6 +1816,27 @@ const artic::Type* TypeDecl::infer(TypeChecker& checker) {
     return type;
 }
 
+const artic::Type* ExtTypeDecl::infer(TypeChecker& checker) {
+    if (!checker.enter_decl(this))
+        return checker.type_table.type_error();
+    const ExtType* ext_type = checker.type_table.ext_type(*this);
+    // Set the type before entering the args
+    type = ext_type;
+    for (auto& arg : args_) {
+        if (auto t = std::get_if<Ptr<Type>>(&arg))
+            args_types_.emplace_back(checker.infer(**t));
+        else if (auto e = std::get_if<Ptr<Expr>>(&arg)) {
+            checker.infer(**e);
+            if (!(*e)->is_constant())
+                checker.error((*e)->loc, "only constants are allowed as external type members");
+            args_types_.emplace_back(nullptr);
+        } else
+            assert(false);
+    }
+    checker.exit_decl(this);
+    return ext_type;
+}
+
 const artic::Type* ModDecl::infer(TypeChecker& checker) {
     for (auto& decl : decls)
         checker.infer(*decl);
diff --git a/src/emit.cpp b/src/emit.cpp
index 83e1f7da..ab53ba5a 100644
--- a/src/emit.cpp
+++ b/src/emit.cpp
@@ -1756,6 +1756,10 @@ const thorin::Def* TypeDecl::emit(Emitter&) const {
     return nullptr;
 }
 
+const thorin::Def* ExtTypeDecl::emit(Emitter&) const {
+    return nullptr;
+}
+
 const thorin::Def* ModDecl::emit(Emitter& emitter) const {
     for (auto& decl : decls) {
         // Do not emit polymorphic functions directly: Those will be emitted from
@@ -1885,8 +1889,17 @@ std::string SizedArrayType::stringify(Emitter& emitter) const {
 }
 
 const thorin::Type* SizedArrayType::convert(Emitter& emitter) const {
-    if (is_simd)
-        return emitter.world.prim_type(elem->convert(emitter)->as<thorin::PrimType>()->primtype_tag(), size);
+    if (is_simd) {
+        auto elem_type = elem->convert(emitter);
+        if (auto prim_type = elem_type->isa<thorin::PrimType>())
+            return emitter.world.prim_type(prim_type->primtype_tag(), size);
+        else if (auto ptr_type = elem_type->isa<thorin::PtrType>())
+            return emitter.world.ptr_type(ptr_type->pointee(), size, ptr_type->addr_space());
+
+        //This should be unreachable after type checking.
+        assert(false);
+        return nullptr;
+    }
     return emitter.world.definite_array_type(elem->convert(emitter), size);
 }
 
@@ -2023,6 +2036,31 @@ const thorin::Type* TypeApp::convert(Emitter& emitter) const {
     return result;
 }
 
+std::string ExtType::stringify(Emitter& emitter) const {
+    if (!type_params())
+        return decl.id.name;
+    return stringify_params(emitter, decl.id.name + "_", type_params()->params);
+}
+
+const thorin::Type* ExtType::convert(Emitter& emitter, const Type* parent) const {
+    if (auto it = emitter.types.find(this); !type_params() && it != emitter.types.end())
+        return it->second;
+
+    auto type = emitter.world.extern_type(decl.type_name, decl.args_types_.size(), { decl.id.name });
+    emitter.types[parent] = type;
+
+    for (size_t i = 0; i < decl.args_types_.size(); i++) {
+        if (auto t = decl.args_types_[i]) {
+            type->set_op(i, t->convert(emitter));
+        } else if (auto e = std::get_if<Ptr<ast::Expr>>(&decl.args_[i]))
+            type->set_op(i, emitter.emit(**e));
+        else
+            assert(false);
+    }
+
+    return type;
+}
+
 // A read-only buffer from memory, not performing any copy.
 struct MemBuf : public std::streambuf {
     MemBuf(const std::string& str) {
diff --git a/src/lexer.cpp b/src/lexer.cpp
index 1f474765..c4f35ca3 100644
--- a/src/lexer.cpp
+++ b/src/lexer.cpp
@@ -23,6 +23,7 @@ std::unordered_map<std::string, Token::Tag> Lexer::keywords{
     std::make_pair("struct",    Token::Struct),
     std::make_pair("enum",      Token::Enum),
     std::make_pair("type",      Token::Type),
+    std::make_pair("type_ext",  Token::TypeExt),
     std::make_pair("implicit",  Token::Implicit),
     std::make_pair("summon",    Token::Summon),
     std::make_pair("static",    Token::Static),
diff --git a/src/parser.cpp b/src/parser.cpp
index 7ea25107..1466c6d6 100644
--- a/src/parser.cpp
+++ b/src/parser.cpp
@@ -42,6 +42,7 @@ Ptr<ast::Decl> Parser::parse_decl(bool is_top_level) {
         case Token::Struct:   decl = parse_struct_decl();   break;
         case Token::Enum:     decl = parse_enum_decl();     break;
         case Token::Type:     decl = parse_type_decl();     break;
+        case Token::TypeExt:  decl = parse_ext_type_decl(); break;
         case Token::Implicit: decl = parse_implicit_decl(); break;
         case Token::Static:   decl = parse_static_decl();   break;
         case Token::Mod:      decl = parse_mod_decl();      break;
@@ -200,6 +201,30 @@ Ptr<ast::TypeDecl> Parser::parse_type_decl() {
     return make_ptr<ast::TypeDecl>(tracker(), std::move(id), std::move(type_params), std::move(aliased_type));
 }
 
+Ptr<ast::ExtTypeDecl> Parser::parse_ext_type_decl() {
+    Tracker tracker(this);
+    eat(Token::TypeExt);
+    auto id = parse_id();
+
+    Ptr<ast::TypeParamList> type_params;
+    // if (ahead().tag() == Token::LBracket)
+    //     type_params = parse_type_params();
+
+    std::vector<std::variant<Ptr<ast::Type>, Ptr<ast::Expr>>> args;
+    expect(Token::Eq);
+    auto type_name = parse_str();
+    expect(Token::LBrace);
+    parse_list(Token::RBrace, Token::Comma, [&] {
+        if (accept(Token::Type))
+            args.emplace_back(parse_type());
+        else
+            args.emplace_back(parse_expr());
+    });
+
+    expect(Token::Semi);
+    return make_ptr<ast::ExtTypeDecl>(tracker(), std::move(id), std::move(type_name), std::move(type_params), std::move(args));
+}
+
 Ptr<ast::ImplicitDecl> Parser::parse_implicit_decl() {
     Tracker tracker(this);
     eat(Token::Implicit);
diff --git a/src/print.cpp b/src/print.cpp
index d28cc940..49111c65 100644
--- a/src/print.cpp
+++ b/src/print.cpp
@@ -614,6 +614,22 @@ void TypeDecl::print(Printer& p) const {
     p << ';';
 }
 
+void ExtTypeDecl::print(Printer& p) const {
+    if (attrs) attrs->print(p);
+    p << log::keyword_style("type_ext") << ' ' <<  id.name;
+    // if (type_params) type_params->print(p);
+    p << " = \"" << type_name << "\" { ";
+    print_list(p, ',', args_, [&] (auto& arg) {
+        if (auto t = std::get_if<Ptr<ast::Type>>(&arg)) {
+            p << **t;
+        } else if (auto e = std::get_if<Ptr<ast::Expr>>(&arg))
+            p << **e;
+        else
+            p << "invalid";
+    });
+    p << " };";
+}
+
 void ModDecl::print(Printer& p) const {
     if (attrs) attrs->print(p);
     bool anon = id.name == "";
@@ -825,6 +841,10 @@ void TypeAlias::print(Printer& p) const {
     p << decl.id.name;
 }
 
+void ExtType::print(Printer& p) const {
+    p << decl.id.name;
+}
+
 void TypeApp::print(Printer& p) const {
     applied->print(p);
     p << '[';
diff --git a/src/types.cpp b/src/types.cpp
index f7e3bf42..7055c8d5 100644
--- a/src/types.cpp
+++ b/src/types.cpp
@@ -726,6 +726,10 @@ const TypeAlias* TypeTable::type_alias(const ast::TypeDecl& decl) {
     return insert<TypeAlias>(decl);
 }
 
+const ExtType* TypeTable::ext_type(const ast::ExtTypeDecl& decl) {
+    return insert<ExtType>(decl);
+}
+
 const Type* TypeTable::type_app(const UserType* applied, const ArrayRef<const Type*>& type_args) {
     if (auto type_alias = applied->isa<TypeAlias>()) {
         assert(type_alias->type_params() && type_alias->decl.aliased_type->type);