Disclosed is a phototransistor comprised of an indium arsenide n-type semiconductor substrate, a thin, relatively lightly doped p-type cadmium diffused region in the substrate forming a photosensitive diode junction, and a metal film in rectifying contact with the p-type diffused region to form a Schottky barrier.The method for fabricating the transistor comprises producing the shallow cadmium diffusion, etching the surface of the diffused region to a predetermined depth to reduce the doping level and the surface oxide level, and depositing the metal film on the etched surface of the diffused region.