Thin SiO2 films were prepared by photochemical vapour deposition. IR absorption and Auger electron spectroscopy showed that the dominant components of the oxide are silicon and oxygen with a small amount of hydrogen. Metal/insulator/semiconductor (MIS) capacitors were constructed on InSb substrates. Capacitance-voltage characteristics of the MIS capacitors were measured, and a midgap interface state density of the order of 1012 cm-2 eV-1 was determined. The amount of hysteresis observed was found to be about 10% of the inversion bias voltage. Annealing studies were also conducted to improve the electrical properties. After annealing, the midgap interface state density was reduced to 5 × 1011 cm-2 eV-1 and the amount of hysteresis reduced to 5% of the inversion bias voltage.