A channel region having a first conductivity type is disposed in a surface portion of a semiconductor substrate. A gate region having a second conductivity type is disposed in a surface portion of the channel region. A first semiconductor region having the second conductivity type is disposed under the channel region. Source/drain regions having the first conductivity type are disposed in parts of the surface portion of the channel region on both sides of the gate region in a channel length direction. Second semiconductor regions each having a high impurity concentration and the second conductivity type are disposed in parts of the semiconductor substrate on both sides of the channel region in a channel width direction.