The thermal oxidation temperature dependence of 4H-silicon carbide (SiC) is systematically investigated using X-ray photoelectron spectroscopy (XPS) and capacitance-voltage (C-V) measurements. When SiC is thermally oxidized, silicon oxycarbides (SiCxOy) are first grown and then silicon dioxide (SiO2) is grown. It is identified by XPS that the SiO2 films fall into two categories, called SiC-oxidized SiO2 and Si-oxidized SiO2 in this paper. The products depend on thermal oxidation temperature. The critical temperature is between 1200 and 1300 degrees C. The interface trap density (D-it) of the sample possessing Si-oxidized SiO2, at thermal oxidation temperature of 1300 degrees C, is lower than SiC-oxidized SiO2 at and below 1200 degrees C, suggesting that a decrease of the C component in SiO2 film and SiO2/SiC interface by higher oxidation temperature improves the metal-oxide-semiconductor (MOS) characteristics. (c) 2006 Elsevier B.V. All rights reserved.