A floating base silicon controlled rectifier is provided, which at least comprises a first conductivity type layer; a second conductivity type well formed in the first conductivity type layer; a first conductivity type heavily doped region coupled to a first node and formed in the second conductivity type well; and a second conductivity type heavily doped region coupled to a second node and formed in the first conductivity type layer. The first conductivity type and the second conductivity type are opposite. When the first conductivity type is N type, the second conductivity type is P type. Alternatively, when the first conductivity type is P type, the second conductivity type is N type. By employing the proposed present invention, the floating base silicon controlled rectifier acts as a forward diode, and an input capacitance can be greatly reduced.