We report the fabrication and properties ofp‐InP:n‐amorphous silicon heterojunctions. The good rectification ratio of 1000:1 at 0.5 V, and existence of straight‐line capacitance curves, indicated a sharp interface of good quality. Optical internal photoemission measurements under various bias conditions showed that the band offsets were 0.06 and 0.37 eV for the valence and conduction bands, respectively. Photovoltaic action resulted in open circuit voltages of over 0.9 V at air mass 2 solar illumination and efficiencies of over 9%.