Interface properties in the MOS system on 4H-SiC(03 (3) over bar8) were investigated using n-type MOS capacitors and inversion-type n-channel MOSFETs. For comparison, the (11 (2) over bar0) and (0001) faces were also examined. High-frequency C-V characteristics at a low temperature (100K) and AC conductance method at room temperature for MOS capacitors revealed the small density of interface states near the conduction band edge on (03 (3) over bar8). N-channel MOSFETs on (03 (3) over bar8) indicated the highest channel mobility among examined crystal orientations of 4H-SiC.