Gate oxides 4 to 50 nm thick have been grown on Si(100) by anodic oxidation at room temperature. Different concentrations of aqueous NH4OH were used, as the electrolyte. Growth of oxides on n-type substrates required light illumination; however, the uniformity of the oxide thickness was not critically dependent on the uniformity of the illumination as long as light saturation conditions were maintained. The oxides on n-type Si were slightly thicker than those on p-type Si under the same growth conditions; nevertheless the physical properties of the oxides grown on the two types of substrates were similar. The growth mechanism was determined by secondary ion mass spectrometry with O-18 labeling, and depends on the solution pH. The as-grown and annealed oxides were characterized by Fourier transform infrared and by HF etch rate experiments. After appropriate annealing, simple metal-oxide-semiconductor capacitors exhibited promising electrical properties.