Reflectance and absorption spectra of photo-CVD SiO2 films in the vacuum ultraviolet (VUV) light region have been measured. The estimated refractive index, n, and extinction coefficient, k, of the film deposited at 177°C in the 5–25 eV region are close to those of fused quartz. The films deposited at 177 and 280°C extend their absorption tails 0.4 eV more to the low energy region than fused quartz. An absorption peak at about 7.6 eV appears and increases with the deposition-temperature. This peak shows a peculiar deposition-temperature dependence as compared with the absorption peaks in the IR region such as Si-H and Si-OH bondings. The interface state density of MOS diodes made from the films deposited by photo-CVD is extremely low and its minimum value is about 2×1010 cm-2 eV-1.