We present an investigation of the degree of oxidization of tungsten oxide (WO
) thin films used as gate dielectric for metal-insulator-semiconductor field-effect transistors (MISFET). By means of X-ray photoelectron spectroscopy WO
thin films grown by pulsed-laser deposition at room temperature were investigated. The electrical and optical properties depend significantly on the oxygen pressure during deposition and are affected by the stoichiometric ratio of oxygen and tungsten.