This work deals with the complex characterisation of oxide semiconductor gas sensor materials, like beta -Ga2O3, WO3 and WO3/TiO2, by DC resistance measurements, impedance spectroscopy, SIMS, DSC and XRD. Impedance spectroscopy was used to study the oxygen/beta -Ga2O3 interaction between 567 and 790 degreesC, (grain size: 30, 150 and 1000 nm), in the context of the bulk and grain boundary conduction phenomena. The mechanism of interaction was investigated also by the SIMS technique. The thermal. structural and electric properties of WO3 and chemically prepared WO3/TiO2 powders as well as thick films were compared by DSC, XRD and DC resistance measurements, in the temperature range of 25-500 degreesC.