The capacitance vs. voltage and current density vs. voltage characteristics of silicon dioxide films formed by anodization of silicon in dilute ammonium hydroxide solutions have been measured. Postoxidation annealing (POA) ai temperatures up to 700-degrees-C greatly reduces the leakage currents and results in breakdown voltages in excess of 10 MV/cm. However, leakage currents are still in excess of those obtained by thermal oxidation, possibly indicating some residual structural imperfection such as a transition layer or roughness at the silicon-silicon dioxide interface. The combination of a POA at 700-degrees-C with a postmetallization anneal in forming gas at 400-degrees-C have reduced the interface state densities to 4 X 10(10) eV-1 cm-2 with fixed charge densities at the interface of -7 x 10(11) charge/cm2.