The heterointerfacep‐CuInSe2/CdS was investigated by soft x‐ray photoelectron spectroscopy. CdS was deposited sequentially in steps onto CuInSe2(011) cleavage planes at room temperature (RT) and at elevated temperatures (≳120 °C). At RT a nonreactive interface to cubic CdS is formed. The valence band and conduction‐band discontinuities are determined to be 0.8 and 0.7 eV, respectively. A band bending of 0.9 eV is deduced for thep‐type substrate. Annealing to temperatures above 120 °C leads to the formation of a CuxS reactive layer at the interface. As a consequence the valence‐band offset and band bending is found to be considerably reduced. The experimentally determined band energy diagram is in agreement with heterojunctions of zincblende‐type semiconductors, and its consequences for solar cells are discussed. ©1995 American Institute of Physics.