A semiconductor device includes a substrate, a gate positioned on the substrate, a drain region and a source region formed in the substrate at two respectively sides of the gate, a first well region formed in the substrate, and a plurality of first doped islands formed in the source region. The drain region and the source region include a first conductivity, and the first well region and the first doped islands include a second conductivity. The source region is formed in the first well region, and the first doped islands are spaced apart from the first well region.