Patent ID: 8232600

Claim:
A semiconductor integrated circuit, comprising: a well of a first conductivity type formed on a semiconductor substrate; a first external terminal, a second external terminal, and a third external terminal provided above the semiconductor substrate; a first protection circuit formed in a first region of the well, having a first impurity diffusion region and a second impurity diffusion region that are both of a second conductivity type and electrically connected to the first external terminal and the second external terminal, respectively; a second protection circuit formed in a second region of the well, having a third impurity diffusion region and a fourth impurity diffusion region that are both of the second conductivity type and electrically connected to the second external terminal and the third external terminal, respectively; a third protection circuit formed in a third region of the well, having a fifth impurity diffusion region and a sixth impurity diffusion region that are both of the second conductivity type and electrically connected to the third external terminal and the first external terminal, respectively; an element isolation region formed in the well to surround the first region, the second region, and the third region; and a guard ring formed continuously in the well to surround at least two regions adjacent to each other, among the first region, the second region, and the third region, via the element isolation region, wherein a plurality of external terminals including the first external terminal, the second external terminal, and the third external terminal, to which P different power supply voltages (P is an integer equal to or more than 3) are respectively supplied, are provided above the semiconductor substrate, N regions including the first region, the second region, and the third region are formed in the well, where N=P(P−1)/2, one protection circuit is provided in each of the N regions, and the guard ring surrounds the entire of the N regions via the element isolation region.