Patent ID: 7309883

Claim:
A semiconductor device comprising: a first well connected to a pad to which an external pin is connected, the first well including a first-type diffusion region connected to a bias voltage terminal; a second well adjacent to the first well, the second well including an insulating region having a first-type diffusion region and at least one second-type diffusion region outside the insulating region, wherein the at least one second-type diffusion region of the second well is connected to a first voltage terminal, and wherein the first-type diffusion region of the insulating region is connected to a second voltage terminal; and a third well adjacent to the second well and including a first-type diffusion region connected to the first voltage terminal, wherein the insulating region inside the second well, the at least one second-type diffusion region of the second well, and the first-type diffusion region of the first well, constitute a bipolar junction transistor which operates in a cut-off mode to cut off current from flowing from the first well to the third well when a control voltage is applied to the second voltage terminal.