Interface states of SiO(2)/4H- and 6H-SiC on the (11 (2) over bar0) and (0001)Si faces were systematically characterized using high-frequency C-V measurements of n-MOS capacitors at 300K and 100K. The interface of SiO(2)/4H-SiC(11 (2) over bar0) formed by wet oxidation has smaller interface state density near the conduction band edge than that of SiO(2)/4H-SiC(0001)Si. The flatband voltage shift and hysteresis in C-V characteristics at 100K revealed different interface properties between the (11 (2) over bar0) and (0001)Si faces. The effects of dry oxidation on interface properties were also investigated.