Cadmium and zinc compositions in Cu 2S formed on Zn x Cd1_x S 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 Cu 2S are generally in the 1018–1019 cm_3 range. 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 Cu 2S surface were measured subsequent to heat treatment, accompanied by increased oxygen. Following heat treatments, Cd and Zn concentrations in the Cu 2S ’’bulk’’ are found to be less than 1019 and 1020 cm_3, respectively, for all substrate compositions used.