a semiconductor device including a gate insulating film selectively formed on a predetermined region of a semiconductor substrate ; a gate electrode formed on said gate insulating film ; and a source region and drain region formed , in a surface portion of said semiconductor substrate , on two sides of a channel region positioned below said gate electrode ; wherein a carbon concentration in an interface where said gate insulating film is in contact with said gate electrode is not more than 5 × 10 22 atoms / cm 3 .