Microelectronic research is highly interested in the achievement of material in thin film form with easily tailoring optical properties. Here, we present a simple low temperature and highly versatile method for obtaining inorganic thin films with variable band gap. The technique that we present allows the elaboration of indium oxysulfide beta-In2S3-3xO3x thin films, whose optical band gap can be tailored between 2 and 3 eV, at low temperature (T-a = 473 K) on glass substrates. They offer the prospect of both new fundamental science and useful technological applications. They are typically produced by physical vapour deposition followed by in situ annealing, The introduction of oxygen into the films during the in situ post-annealing process is shown to be crucial for the growth of variable optical band gap material. The variation of the substrate temperature, T-S, during the deposition allows to manage the band gap value. It is shown that this effect is related to the introduction of oxygen into the films. (C) 2002 Elsevier Science B.V. All rights reserved.