The modification of chemically deposited ZnSe thin films of approximately 0.3 mum thickness by ion exchange in dilute solutions 0.001 M-0.025 M of CuCl2 has been investigated. The ion exchange reaction, as studied by XPS depth profile analysis, shows Cu/Zn ratios of 0.32 and 90 for a 90 s ion exchange in 0.001 M CuCl2 and a 3 min ion exchange in 0.01 M CuCl2, respectively. Following ion exchange, the binding energies are measured as 952 eV for Cu 2p1/2, 932 eV for Cu 2p3/2 and 54.5 eV for Se 3d5/2. The corresponding values for CuSe thin film deposited directly from a chemical bath are 952, 932.5 and 55 eV. Optical transmittance spectra and sheet resistance measurements of the ion-exchanged films compare favourably with directly deposited CuSe thin films, which indicates the formation of CuSe. These results demonstrate that thin films of semiconducting materials can be prepared in a simple manner by ion exchange.