Undoped silicate glass deposited using the tetraethylorthosilicate (TEOS) and ozone thermal reaction has been selected as one of the candidates for shallow trench isolation applications. As a replacement for existing low pressure or atmospheric pressure chemical vapor deposition processes for device dimensions below 0.25 mu m, TEOS/ozone films deposited at high temperature (>550 degrees C) exhibit the superior qualities in terms of void-free trench fill. In this paper, we present some characterization of the silicon oxide film deposited in the subatmospheric pressure regime using TEOS/ozone chemistry, aimed at developing a high-quality dielectric film to meet shallow trench isolation gap-fill requirements. It is also identified that low ozone/TEOS ratio reduces surface and pattern sensitivity. Therefore, no additional treatment or predeposition is necessary. Moreover, to enhance the etch resistance of the silicon oxide, the as-deposited film is annealed at high temperature for densification and bond reconstruction.