Surface and bulk composition of ZnSe thin films deposited by the chemical bath deposition (CBD) method, are analyzed with x-ray photoelectron spectroscopy (XPS). In-depth composition information is obtained with angle-resolved XPS (ARXPS) and sputtering-assisted XPS. The films show excess Zn proportion (Zn/Se=1.1) due to an amount of ZnO (or OH−). ARXPS and sputtering assisted measurements show that the Zn excess is higher in the layers closer to the substrate, i.e., layers deposited at the beginning of the deposition process. A deposition mechanism most active at the beginning is responsible for the competitive deposition of ZnO. Other minority components in the films are surface SeO2, from ZnSe oxidation in air, bulk atomic Se, from oxidation of ZnSe and/or selenide bath precursors, and atomic Zn on layers closer to the substrate surface, from the initial CBD reaction. © 2002 American Vacuum Society.