A semiconductor device is disclosed, including a plurality of gate rings formed on a substrate and concentrically surrounding a first doped region formed in the substrate. The gate rings are equipotentially interconnected by at least a connecting structure. A second doped region is formed in the substrate, exposed from the space between adjacent gate rings. A third doped region is formed in the substrate adjacent to the outer perimeter of the outermost gate ring. The first doped region, the third doped region and the gate rings are electrically biased and the second doped regions are electrically floating.