A semiconductor device for electrostatic discharge protection includes a substrate, a first well and a second well formed in the substrate. The first and second wells are formed side by side, meeting at an interface, and have a first conductivity type and a second conductivity type, respectively. A first heavily doped region and a second heavily-doped region are formed in the first well. A third heavily doped region and a fourth heavily-doped region are formed in the second well. The first, second, third, and fourth heavily-doped regions have the first, second, second, and first conductivity types, respectively. Positions of the first and second heavily-doped regions are staggered along a direction parallel to the interface.