A semiconductor device includes a second conductivity type layer selectively formed by changing impurity concentrations on a semiconductor substrate, a first conductivity type source region formed on the second conductivity type layer, a first conductivity type drain region formed on the second conductivity type layer apart from the first conductivity type source region, a gate electrode formed between the first conductivity type source region and the first conductivity type drain region across an insulation film, and a second conductivity type contact layer formed adjacent to the first conductivity type source region, wherein the second conductivity type layer in the source region side has a higher impurity concentration than the impurity concentration of the second conductivity type layer in the drain region side.