The electrical properties of pseudomorphic epilayer–epilayer ZnSe/GaAs heterointerfaces, grown by molecular‐beam epitaxy, have been investigated by capacitance versus voltage (C–V) and current versus voltage measurements. Undoped stoichiometric ZnSe (<1000 Å), exhibiting high resistivity, performs the function of the insulator in these metal–insulator–semiconductor capacitors. TheC–Vcharacteristics of the annealed Au/ZnSe/p‐GaAs capacitors are nearly ideal, exhibiting an interface state density (2.5×1011cm−2) which compares favorably with the densities reported at typical (Al,Ga)As interfaces. The occurrence of both hole accumulation (forp‐type GaAs) and inversion (forn‐type GaAs) at the ZnSe/GaAs heterointerface indicates the presence of a substantial valence‐band offset. The lack of accumulation or inversion layers for electrons suggests a relatively small conduction‐band discontinuity.