Interfacial characteristics of Al/SiO2/n-type 6H-SiC metal-oxide-semiconductor capacitors fabricated by rapid thermal processing (RTP) with N2O and NO annealing are investigated. Interface state density was measured by a conductance technique at room temperature. RTP oxidation in pure O2 leads to an excellent SiO2/n-type 6H-SiC interface with interface state density in the order of 1010-1011 eV-1 cm-2. NO annealing improves the SiO2/n-type 6H-SiC interface, while N2O annealing increases the interface state density.