Zinc sulphide thin films are deposited on SnO2/glass using the chemical bath deposition technique. X-ray diffraction and atomic force microscopy are used to characterize the structure of the films; the surface composition of the films is studied by Auger electrons spectroscopy, the work function and the photovoltage are investigated by the Kelvin method. Using these techniques, we specify the effect of pH solution and heat treatment in vacuum at 500 degrees C. The cubic structure corresponding to the (1 1 1) planes of beta-ZnS is obtained for pH equal to 10. The work function (Phi(material) - Phi(probe)) for ZnS deposited at pH 10 is equal to -152 meV. Annealing at 500 degrees C increases Phi(m) (by about 43 meV) and induces the formation of a negative surface barrier. In all cases, Auger spectra indicate that the surface composition of zinc sulphide thin films exhibits the presence of the constituent elements Zn and S as well as C and O as impurity elements. (C) 2008 Elsevier B.V. All rights reserved.