A semiconductor device includes a semiconductor substrate and a semiconductor layer formed thereover. A gate structure is disposed over the semiconductor layer, and a first doped region is disposed in the semiconductor layer adjacent to a first side of the gate structure. A second doped region is disposed in the semiconductor layer adjacent to a second side of the gate structure opposite to the first side. A third doped region is disposed in the first doped region. A fourth doped region is disposed in the second doped region. A plurality of fifth doped regions is disposed in the second doped region. A sixth doped region is disposed in the semiconductor layer under the first doped region. A conductive contact is formed in the third doped region and the first doped region.