CuInS2 thin films have been deposited by chemical spray pyrolysis at 650 K and heat-treated under a sulfur atmosphere for I h at the same temperature. The effect of this treatment on the properties of the films was studied by X-ray diffraction, electron microprobe analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, optical and electrical measurements. The changes in the properties, mainly the electrical, are attributed to the fact that the oxygen, originally present at the grain boundaries and linked to indium, is replaced by sulfur: the ln(2)O(3) is then removed from the grain boundaries. The treated films are therefore more suitable for solar cell applications, where transversal parasitic effects are an important issue. (C) 2002 Published by Elsevier Science B.V.