Two-step nitric acid oxidation which involves immersion in similar to 40 wt % HNO3 followed by immersion in 68 wt % HNO3 at 121 degrees C can form a thick (e.g., 10 nm) SiO2 layer on a 3C-SiC surface. Heat-treatment at 400 degrees C in pure hydrogen performed after nitric acid oxidation greatly decreases the density of the leakage current flowing through the SiO2 layer. The hydrogen treatment effectively smoothens the SiO2/SiC interface. When the hydrogen treatment at 400 degrees C is performed before nitric acid oxidation, the SiC surface is greatly flattened and the subsequent nitric acid oxidation results in the SiO2/SiC interface having an atomic flatness. Without hydrogen treatment, SiO2 gap states are present up to 1.5 eV from the SiO2 valence-band maximum, and the valence-band discontinuity energy at the SiC/SiO2 interface is 3.0 eV. With the hydrogen treatment before nitric acid oxidation, the SiO2 gap states disappear and the valence-band discontinuity energy increases to 3.9 eV. Capacitance-voltage curves of the metal-oxide-semiconductor (MOS) diodes in which hydrogen treatment is performed before nitric acid oxidation show typical accumulation and depletion behavior. (c) 2007 The Electrochemical Society.