Semiconductor device having breakdown voltage enhancement structure

Abstract(summary):

A semiconductor device includes a substrate of a first conductivity type, a first impurity region of a second conductivity type formed on a top surface side of the substrate, a second impurity region of the second conductivity type formed on the top surface side of the substrate and in contact with the first impurity region, the second impurity region laterally surrounding the first impurity region and having a greater depth than the first impurity region, as viewed in cross-section, and a breakdown voltage enhancing structure of the second conductivity type formed to laterally surround the second impurity region. A boundary between the first and second impurity regions has a maximum impurity concentration equal to or less than that of the second impurity region, and a current is applied between a top surface and a bottom surface of the substrate.