Patent ID: 7064392

Claim:
A semiconductor device having an input/output protection circuit section on a semiconductor substrate, the input/output protection circuit section comprising: a plurality of field effect transistors connected in parallel, each of which has a source diffusion layer of a first conductive type and a drain diffusion layer of the first conductive type, a channel region therebetween and a gate electrode that is disposed between said source and drain diffusion layers; a dopant diffusion region of a second conductive type that is set at a distance from said plurality of field effect transistors; and an element isolation film located in the substrate between the dopant diffusion region of the second conductive type and the source diffusion layer of the first conductive type, for separating the dopant diffusion region from the source diffusion layer, wherein said dopant diffusion region is connected to a reference potential, and wherein the source diffusion layer is also connected to said reference potential, wherein the drain diffusion layer is connected directly to an input/output terminal section without an intervening resistance element, wherein a first conductive type well having a lower dopant concentration than the dopant concentration of the source diffusion layer is formed directly under the source diffusion layer and thereby the first conductive type well is electrically connected directly with the source diffusion layer, wherein no first conductive type well is formed under or connected to the drain diffusion layer, wherein the first conductive type well at least partially underlies the element isolation film, and wherein a second conductive type well is formed on the surface of the semiconductor substrate, said source and drain diffusion layers of the first conductive type and said dopant diffusion region of the second conductive type are disposed over the second conductive type well, and thereby the dopant diffusion region of the second conductive type is electrically connected directly with the second conductive well, but the first conductive well is not physically contacted directly with the dopant diffusion region of the second conductive type.