p contact region 4 an ion implantation mask material is patterned on the surface of n u2212 drift layer 2 the p type base region 3 and the p contact region 4 nitrogen is ion implanted thereto for forming an n source region 5 after forming the n source region 5 an ion implantation mask material is patterned and nitrogen is ion implanted only to the n u2212 drift layer 2 channel region according to the procedure nitrogen is introduced to the channel region after removing the ion implantation mask material a heat treatment at 1 700 u00b0 c is performed for activating al and nitrogen thus implanted a first gate dielectric film 6 a is then formed by thermal oxidation within a process temperature range of approximately from 1 000 to 1 300 u00b0 c the first gate dielectric film 6 a may be formed with no gas or n 2 o gas according to the procedure nitrogen is introduced to the interface between the sic substrate and the gate dielectric film the first gate dielectric film 6 a has a thickness of 3 nm or more a metal oxide film 6 b and a second gate dielectric film are then formed sequentially the thickness of the metal oxide film 6 b is 10 or less of the total thickness of the gate dielectric film 6 the total thickness of the gate dielectric film 6 is.