Indium sulfide (In2S3) thin films have been prepared by the spray pyrolysis (SP) technique using indium acetate and N-N dimethyl thiourea as precursor compounds. Samples prepared at different temperatures and atomic ratio of In to S in the starting solution, (In/S)(sol), have been characterized using several techniques. X-ray diffraction studies have shown that the preparation temperature (T-p) affects the crystallinity of the deposited materials as well as the optoelectronic properties. For (In/S)(sol)=1/8, the optical band gap (E,) increases from 2.2 up to 2.67 eV when T-p increases from 250 up to 450 degrees C. For (In/S)(sol)=1 and T-p=450 degrees C, the deposited material shows n-type electrical conductivity with a dark value of 1 (Omega cm)(-1), and E-g=2.04 eV. The In2S3 thin films prepared under these conditions have a big potential use as a window material for photovoltaic heterojunction devices. (c) 2004 Published by Elsevier B.V.