diff --git a/src/swc/__tests__/options.test.ts b/src/swc/__tests__/options.test.ts
index 534a96a..a352db9 100644
--- a/src/swc/__tests__/options.test.ts
+++ b/src/swc/__tests__/options.test.ts
@@ -33,6 +33,7 @@ const createDefaultResult = (): ParserArgsReturn => ({
     outDir: undefined,
     // @ts-expect-error
     outFile: undefined,
+    outFileExtension: "js",
     quiet: false,
     sourceMapTarget: undefined,
     stripLeadingPaths: false,
@@ -63,6 +64,29 @@ describe("parserArgs", () => {
     expect(result).toEqual(defaultResult);
   });
 
+  describe("--out-file-extension", () => {
+    it("provides the extension in the parsed args", () => {
+      const args = [
+        "node",
+        "/path/to/node_modules/swc-cli/bin/swc.js",
+        "src",
+        "--out-file-extension",
+        "magic_custom_extension",
+      ];
+      const result = parserArgs(args);
+      const expectedOptions = deepmerge(defaultResult, {
+        cliOptions: { outFileExtension: "magic_custom_extension" },
+      });
+      expect(result).toEqual(expectedOptions);
+    });
+
+    it("provides the a sensible default", () => {
+      const args = ["node", "/path/to/node_modules/swc-cli/bin/swc.js", "src"];
+      const result = parserArgs(args);
+      expect(result.cliOptions.outFileExtension).toEqual("js");
+    });
+  });
+
   describe("errors", () => {
     let mockExit: jest.SpyInstance;
     let mockConsoleError: jest.SpyInstance;
diff --git a/src/swc/dir.ts b/src/swc/dir.ts
index f4cefd0..26949cb 100644
--- a/src/swc/dir.ts
+++ b/src/swc/dir.ts
@@ -60,6 +60,7 @@ async function initialCompilation(cliOptions: CliOptions, swcOptions: Options) {
     copyFiles,
     extensions,
     outDir,
+    outFileExtension,
     stripLeadingPaths,
     sync,
     quiet,
@@ -92,6 +93,7 @@ async function initialCompilation(cliOptions: CliOptions, swcOptions: Options) {
           sync,
           cliOptions,
           swcOptions,
+          outFileExtension,
         });
         results.set(filename, result);
       } catch (err: any) {
@@ -119,7 +121,14 @@ async function initialCompilation(cliOptions: CliOptions, swcOptions: Options) {
       Promise.allSettled(
         compilable.map(filename =>
           workers
-            .run({ filename, outDir, sync, cliOptions, swcOptions })
+            .run({
+              filename,
+              outDir,
+              sync,
+              cliOptions,
+              swcOptions,
+              outFileExtension,
+            })
             .catch(err => {
               console.error(err.message);
               throw err;
@@ -208,6 +217,7 @@ async function watchCompilation(cliOptions: CliOptions, swcOptions: Options) {
     extensions,
     outDir,
     stripLeadingPaths,
+    outFileExtension,
     quiet,
     sync,
   } = cliOptions;
@@ -252,6 +262,7 @@ async function watchCompilation(cliOptions: CliOptions, swcOptions: Options) {
             sync,
             cliOptions,
             swcOptions,
+            outFileExtension,
           });
           if (!quiet && result === CompileStatus.Compiled) {
             const end = process.hrtime(start);
diff --git a/src/swc/dirWorker.ts b/src/swc/dirWorker.ts
index 102cb33..9ecdbf5 100644
--- a/src/swc/dirWorker.ts
+++ b/src/swc/dirWorker.ts
@@ -13,12 +13,13 @@ export default async function handleCompile(opts: {
   sync: boolean;
   cliOptions: CliOptions;
   swcOptions: Options;
+  outFileExtension: string;
 }) {
   const dest = getDest(
     opts.filename,
     opts.outDir,
     opts.cliOptions.stripLeadingPaths,
-    ".js"
+    `.${opts.outFileExtension}`
   );
   const sourceFileName = slash(relative(dirname(dest), opts.filename));
 
diff --git a/src/swc/options.ts b/src/swc/options.ts
index b64675a..ba57f00 100644
--- a/src/swc/options.ts
+++ b/src/swc/options.ts
@@ -81,6 +81,11 @@ export const initProgram = () => {
     "Compile an input directory of modules into an output directory"
   );
 
+  program.option(
+    "--out-file-extension [string]",
+    "Use a specific extension for the output files [default: js]"
+  );
+
   program.option(
     "-D, --copy-files",
     "When compiling a directory copy over non-compilable files"
@@ -176,6 +181,7 @@ export interface CliOptions {
   readonly extensions: string[];
   readonly watch: boolean;
   readonly copyFiles: boolean;
+  readonly outFileExtension: string;
   readonly includeDotfiles: boolean;
   readonly deleteDirOnStart: boolean;
   readonly quiet: boolean;
@@ -294,6 +300,7 @@ export default function parserArgs(args: string[]) {
     extensions: opts.extensions || DEFAULT_EXTENSIONS,
     watch: !!opts.watch,
     copyFiles: !!opts.copyFiles,
+    outFileExtension: opts.outFileExtension || "js",
     includeDotfiles: !!opts.includeDotfiles,
     deleteDirOnStart: Boolean(opts.deleteDirOnStart),
     quiet: !!opts.quiet,