This paper presents that the channel mobility of 4H-SiC MOSFETs is significantly improved using the buried channel (BC) structure. The BC region was formed by nitrogen ion implantation at room temperature and following rapid thermal annealing. The effects of the depth of BC region and the thermal oxidation condition of the gate oxide on the channel mobility and threshold voltage were investigated. With the nitrogen concentration of 1 x 10(17) cm(-3), the optimal depth of the BC region was found to be 0.2 mum. When the gate oxide was grown by dry oxidation and following wet re-oxidation, the channel mobility of 140 cm(2)/Vs was achieved in the normally-off 4H-SiC BC MOSFET. This channel mobility is the highest reported for a normally-off MOSFET with a thermally grown gate oxide formed on 4H-SiC (0001) wafer.