The x-ray interference technique has been applied to evaluate the structural changes of high temperature grown chemical vapor deposited (CVD)SiO2film under several post annealing conditions. In annealing above 800 °C inO2ambient, a thermal oxide growth has been found at the CVDSiO2/Siinterface, and its precise thicknesses have been determined. The estimated diffusion coefficient of the oxidant in CVD film was about three times larger compared to that of thermal oxide. A threshold voltage shift in the oxide was found to strongly correlate to the thickness of the thermal oxide rather than to thermal modifications of the CVDSiO2itself. ©1997 American Institute of Physics.