Cadmium and zinc compositions in Cu2S formed on ZnxCd1−xS films (0<x≲0.25) by means of ion exchange have been measured using Auger Electron Spectroscopy (AES), Atomic Absorption Spectroscopy (AAS), and Electron Spectroscopy for Chemical Analysis (ESCA). Net concentrations of Cd and Zn in as‐formed Cu2S are generally in the 1018–1019cm−3range. Heat treatments in both oxidizing and reducing ambients raise the concentrations by over an order of magnitude, with the Zn concentrations increasing more so than those of Cd. Large increases in Zn at or near the Cu2S surface were measured subsequent to heat treatment, accompanied by increased oxygen. Following heat treatments, Cd and Zn concentrations in the Cu2S ’’bulk’’ are found to be less than 1019and 1020cm−3, respectively, for all substrate compositions used.