AbstractAlthough low‐cost solar cells based on Se have recently been examined, there have been extremely little basic data which provide a guideline for the improvement of energy conversion efficiency. In this paper, to clarify the behavior of heterojunctions between Se and conductive oxides, an ITO/Se heterojunction has been fabricated and its basic electrical characteristics and impurity concentration distribution by x‐ray photoelectron spectroscopy have been studied. The ITO/Se heterojunction can be regarded as a Schottky contact based on capacitance‐voltage (C‐V) and photoelectric response characteristics. Also, in the current density‐voltage (J‐V) characteristics, the slope of lnJvs.Vis constant regardless of temperature. This has been explained in terms of the tunneling mechanism through interface states; Te (20 Å) introduced at the ITO/Se interface not only prevents the peeling of Se film during the thermal crystallization process, but also improves the diffusion potential and the barrier height by 10%. Although a part of the Te thermally diffused into Se layer forms an acceptor level and changes the impurity doping distribution, it does not especially affect the energy band, theJ‐Vcharacteristics or the spectral response. Since the diffusion potential determined from theC‐Vcharacteristics is approximately 1.5 times the open circuit voltage under AM illumination, this implies that SIS (Semiconductor‐Insulator‐Semiconductor) structures are more suitable for