Thin films (40-60 nm) prepared by co-evaporation of Sn and TeO2 were studied as ethanol gas sensors. In the as-deposited state, the films thus obtained are amorphous and consist of mixed Te and Sn oxides, doped with Te, Sn, and/or SnTe (depending on the atomic ratio between Sn and Te (RSn/Te)), due to interaction between the two substances during the co-deposition. After stepwise thermal treatment of films with RSn/Te ≈ 2.3 up to 360oC (by 40oC steps, for 15 minutes at each temperature) nanocrystalline films, built up of a mixture of SnO2, TeO2 and unstoichiometric Sn oxide were obtained. The Pt-doping was realized by thermal evaporation in a separate vacuum cycle, after the annealing. To study the film composition and structure as well as the volume distribution of the elements different electron microscopy techniques (TEM, SAED) and analytical methods (EDS in SEM, AES) were applied. The sensitivity towards ethanol vapours was investigated as a function of the substrate temperature (T) in the range from 20oC to 200oC. High sensitivity has been observed for Pt-doped films at T = 120oC. No cross sensitivity to relative humidity (RH [%]) was observed at this temperature. Further improvement of the sensitivity could be obtained by optimization of the thermal processing, Pt-doping and working temperature.