Thin films of SnO2 are deposited by an electron beam evaporation method under controlled deposition conditions. The effect of substrate temperature and post-deposition annealing temperature on the structural properties of the films are studied to obtain good SnO2 films for gas sensor application. Scanning electron microscopy results show that the films deposited by this method are uniform and continuous after annealing. It is observed from the X-ray diffraction (XRD) results that the films deposited at lower substrate temperatures are amorphous and become polycrystalline SnO at 350 °C. The films, when annealed, reach the final oxidation state SnO2 either through the single oxidation state SnO or through two oxidation states SnO and Sn3O4, depending on the deposition temperature. It is further observed from XRD and transmission electron microscopy results that the films deposited at 25 and 350 °C and annealed at 600 °C are pure polycrystalline SnO2 films with a larger grain size, which are expected to be suitable for gas sensor application. The films deposited at intermediate substrate temperatures and annealed at 600 °C exhibit mixed phases, with a smaller grain size.