A semiconductor structure includes a substrate, a first well having a first conductive type, a second well having a second conductive type, a body region, a first doped region, a second doped region, a third doped region and a field plate. The first and second wells are formed in the substrate. The body region is formed in the second well. The first and second doped regions are formed in the first well and the body region, respectively. The second and first doped regions have the same polarities, and the dopant concentration of the second doped region is higher than that of the first doped region. The third doped region is formed in the second well and located between the first and second doped regions. The third and first doped regions have reverse polarities. The field plate is formed on the surface region between the first and second doped regions.