Semiconductor device showing at least three successive zones of alternate opposite conductivity type

Claim 1

A semiconductor device having at least a first, second and third successive region of alternate opposite conductivity type forming a first pn-junction between said first and second regions and a second pn-junction between said second and third regions, an annular region inserted within said second region between said first and second pn-junctions, said annular region being of opposite conductivity type to said second region and forms a third pn-junction between said annular region and said second region, comprising: a fourth region formed within said third region, said fourth region being of opposite conductivity type to said third region, said fourth region forming a fourth pn-junction with said third region; and electrode means for electrically connecting said fourth region directly to said annular region so that when A reverse biasing potential is applied to said third region, said third and fourth pn-junctions are connected in series and said second, third and fourth pn-junctions are reversed biased, whereby the potential drop across said third pn-junction is less than the potential drop across said second pn-junction.