A silicon controlled rectifier includes a P-type substrate, an N-type doped well, a first P-type strip-shaped heavily-doped area arranged in the N-type doped well, a first N-type strip-shaped heavily-doped area arranged in the P-type substrate, and at least one N-type heavily-doped area arranged in the P-type substrate and the N-type doped well. The at least one N-type heavily-doped area is not arranged between the first P-type strip-shaped heavily-doped area and the first N-type strip-shaped heavily-doped area, thus the surface area of a semiconductor substrate can be reduced. The conductivity types of the abovementioned components are alternatively changed.