A semiconductor device includes a substrate of a first conductivity type, a gate electrode on the substrate, a first high concentration impurity region of the first conductivity type that is disposed on a first side of the gate electrode, a first well of the first conductivity type that is disposed under the first high concentration impurity region and surrounds the first high concentration impurity region, a second well of a second conductivity type that overlaps with a portion of the gate electrode and is adjacent to the first well, and a first deep well of the second conductivity type that is disposed under the first well and the second well, the first deep well and the first high concentration impurity region being responsive to a first voltage.