A metal oxide semiconductor field effect transistor includes a semiconductor substrate; a well region containing an impurity of a first conductivity type disposed 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. The well region is composed of an epitaxial layer, and the epitaxial layer includes an impurity layer of the first conductivity type having a different impurity concentration.