A semiconductor device includes a substrate including a P-well region, a gate electrode on the substrate, and a first region and a second region formed in the substrate on opposite sides adjacent to the gate electrode, the first region includes a first N-well region in the substrate and a second N-well region, a first impurity region, a second impurity region in the first N-well region, the second region includes a third impurity region in the substrate and a fourth impurity region in the third impurity region, a doping concentration of the second N-well region is greater than a doping concentration of the first N-well region, and a doping concentration of the second impurity region is greater than a doping concentration of the second N-well region.