The knowledge of the interdependence between the structural, thermal and electric properties of oxide semiconductors contributes to widen their practical application. In this work the thermal behaviour of WO3 and WO3/TiO2 powders and thick films - studied by DSC - is compared with the results of X-ray diffraction (XRD) investigation in the temperature range 25-500 degreesC. The X-ray analyses show a reversible phase transition (from gamma -WO3 into beta -WO3) both in WO3 and in WO3/TiO2. However, while in the WO3 the transition takes place between 300 and 400 degreesC, in the WO3/TiO2 system it is not complete even at 400 degreesC, during the measurement time. The phase transition in the WO3 was identified between 320 and 360 degreesC also by DSC, but in the bicomponent material no sharp transition could be detected. This may mean that titanium can thermally stabilize the WO3, influencing also its electric properties.