A semiconductor device and a forming method thereof, the semiconductor device includes a first and a second wells, a source region, a drain region, two gate structures and at least one doping region. The first well with a first conductive type is disposed in a substrate, and the source region is disposed in the first well. The second well with a second conductive type is disposed adjacent to the first well in a substrate, and the drain region is disposed in the second well. Two gate structures are disposed on the substrate between the source region and the drain region. At least one doping region with the first conductive type is disposed in the second well between the two gate structures.