Power mosfet with decreased body resistance under source region

Abstract

A power MOS transistor in which a source region pattern is formed such that the body resistance of a lower portion of a source region is reduced, to thereby suppress turn-on of a parasitic bipolar transistor and equalize the flow of the current. A source region of a first conductivity type includes a first source region loop formed around a source contact without contacting the source contact and a second source region connecting the first source region, contacting the source contact. The first source region is a region from a predetermined region of a lower portion of a gate electrode to the source contact, so that the length of the first source region is shortened. A heavily-doped region of a second conductivity type is symmetrically formed between the first source region and the second source region. Thus, reverse current partially flows to the source electrode via a base region of a lower end of the first source region and the heavily-doped region of the second conductivity type, and the voltage drop is reduced in accordance with the reduction of the length of the first source region to suppress turn-on of the parasitic bipolar transistor. The heavily-doped regions of the second conductivity type are symmetrically formed, to thereby allow the uniform flow of current.