A silicon-controlled rectifier includes a substrate of a first conductivity type; a deep well region of a second conductivity type; a well regions of the first conductivity type and the second conductivity type; a first, second and third heavily doped active regions of the first conductivity type; a first, second and third heavily doped active regions of the second conductivity type; and a first, second and third shallow trench isolation structures. A reverse diode formed in the third heavily doped active region of the second conductivity type and the well region of the first conductivity type is embedded, and a forward diode is formed in the heavily doped active region of the first conductivity type and the well region of the second conductivity type. By sharing the third heavily doped active region of the second conductivity type across the well regions of different conductivity types, two back-to-back diodes are formed.