The electrical properties and the structure of the buried oxide in low dose SIMOX wafers were investigated after 1200 °C oxidation in different diluted oxygen ambients. The thickness of the silicon dioxide grown on top of the thin silicon films was the same for all samples. Correlating the breakdown field and the surface structure of the buried oxide with process conditions showed that the oxidation time was the key parameter for improving oxide performance while the oxygen partial pressure only played a minor role. We suggest that saturation of atomic oxygen in the thin silicon film during oxidation is responsible for this behavior. ©1997 American Institute of Physics.