A semiconductor device suitable for a source-follower circuit, provided with a gate electrode formed on a semiconductor substrate via a gate insulation film, a first conductivity type layer formed in the semiconductor substrate under a conductive portion of the gate electrode and containing a first conductivity type impurity, first source/drain regions of the first conductivity type impurity formed in the semiconductor substrate and extended from edge portions of the gate electrode, and second source/drain regions having a first conductivity type impurity concentration lower than that in the first source/drain regions and formed adjoining the gate insulation film and the first source/drain regions in the semiconductor substrate so as to overlap portions of the conductive portion of the gate electrode.