A semiconductor device according to the present invention includes a semiconductor substrate; device isolation regions provided in the semiconductor substrate; a first conductivity type semiconductor layer provided between the device isolation regions; a gate insulating layer provided on an active region of the first conductivity type semiconductor layer; a gate electrode provided on the gate insulating layer; gate electrode side wall insulating layers provided on side walls of the gate electrode; and second conductivity type semiconductor layers provided adjacent to the gate electrode side wall insulating layers so as to cover a portion of the corresponding device isolation region, the second conductivity type semiconductor layers acting as a source region and/or a drain region. The gate electrode and the first conductivity type semiconductor layer are electrically connected to each other. The second conductivity type semiconductor layers are provided above the first conductivity type semiconductor layer and have a thickness which gradually increases from the device isolation region toward the gate electrode.