A chemical vapor deposition method capable of depositing high‐quality epitaxial layers of CdS on single‐crystal substrates has been employed for the fabrication of heterojunction photovoltaic devices of the typen‐CdS/p‐InP,n‐CdS/p‐CdTe,n‐CdS/p‐GaAs, andn‐CdS/p‐Ge. Analysis of the photovoltaic responses shows that all the devices generally have good collection efficiency, i.e., that at zero bias, photogenerated carriers crossing the junction do not suffer appreciable recombination at interface states. The solar energy conversion efficiency is, however, strongly influenced by the interface states through the open circuit voltage and the fill factor. Analysis of the dark current‐voltage characteristics shows the existence of a low‐temperature low‐bias voltage tunneling current in all of the devices. In at least two devices,n‐CdS/p‐InP andn‐CdS/p‐CdTe, there exists, at temperatures equal to or higher than 300 °K, a tunneling recombination current which flows through states near or at the interface with a thermal activation energy of about 0.6 eV.