Tunnel oxide (SiOx) films, about 20 AA in thickness, were grown on (100) and (111) oriented, 10 Omega cm, p-type silicon wafers at a temperature of 250 degrees C, and pressure of 2 atm in dry oxygen ambient. The SiO x films were characterized using AlSiOx/p-Si MIS diodes with semi-transparent metal electrodes, by variable illumination current-voltage technique. The open-circuit voltage, short-circuit current, ideality factor and reverse saturation current were studied as functions of oxidation time and were found to be in accordance with a reduction of the interface state density with the oxide growth. From the experimental n-values the interface state densities were calculated and were found to be of the order of 1012 cm -2 eV-1 for both orientations. The reverse saturation current density obtained was of the order of 10-7 A cm-2 for (111) oriented substrates and 10-8 A cm-2 for the (100) orientation. The order of the oxide fixed charge was computed using deviation in the experimental barrier height from the theoretical barrier height (assuming no fixed charges are present). This was found to be of the order of 1012 cm-2 in both cases.