Patent ID: 7671424

Claim:
A metal oxide semiconductor field effect transistor comprising: a semiconductor substrate, the semiconductor substrate containing an impurity of a first conductivity type impurity; a well region containing an impurity of the first conductivity type on the semiconductor substrate, the well region including a source region and a drain region formed by adding an impurity of a second conductivity type, the source region and the drain region being separated from each other by a predetermined gap; an insulating film disposed on the surface of the well region in the gap between the source region and the drain region; and a gate electrode disposed on the insulating film, wherein, the impurity concentration of the well region is higher than the impurity concentration of the semiconductor substrate, and the well region is composed of an epitaxial layer, and the epitaxial layer includes an impurity layer therein, the impurity layer being of the first conductivity type and having an impurity concentration different than the other regions of the well region.