A semiconductor device includes a P-type substrate, a P-type well region, an N-type well region, an N-type guard ring region, an insulating layer, a poly gate disposed, and a bulk region. The P-type well region is disposed on the P-type substrate and includes source regions and drain regions each spaced apart from the other. The N-type well region disposed and spaced apart from the P-type well region on the P-type substrate. The N-type guard ring region is disposed around perimeters of the P-type well region and the N-type well region. The insulating layer is disposed around the P-type well region and the N-type well region on the N-type guard ring region. The poly gate is disposed around the perimeter of the P-type well region and the N-type well region, respectively, on the insulating layer. The bulk region is disposed on the N-type guard ring region adjacent the poly gate.