A MOS transistor with self-aligned source/drain terminals, and methods for its manufacture. The transistor generally includes an electrically functional substrate, a dielectric film on portions of the substrate, a gate on the dielectric film, and polycrystalline source and drain terminals self-aligned with the gate. The method generally includes forming an amorphous semiconductor material on a gate and on exposed portions of an electrically functional substrate, irradiating an upper surface of the amorphous semiconductor material to form self-aligned polycrystalline semiconducting source/drain terminal layers, and (optionally) selectively removing the non-irradiated amorphous semiconductor material portions. The present invention advantageously provides MOS thin film transistors having reliable electrical characteristics quickly, efficiently, and/or at a low cost by eliminating one or more conventional photolithographic steps.