Patent ID: 7649213

Claim:
A semiconductor device comprising: a silicon carbide substrate having a first main surface and a second main surface extending in parallel with each other, a direction of a normal of the substrate being off at an off angle from a <0001> or <000-1> direction in an off direction; a silicon carbide layer of a first conductivity type formed on the first main surface of the silicon carbide substrate; a junction forming region formed in a substantially central portion of an upper surface region of the silicon carbide layer; a junction termination region formed so as to surround the junction forming region in the upper surface region of the silicon carbide layer, and including a semiconductor region of a second conductivity type formed as a substantially quadrangular doughnut ring, which has two edges facing each other with the junction forming region interposed therebetween and each crossing a projection direction, which is obtained when the off direction is projected on the upper surface region of the silicon carbide layer, at a right angle, wherein a width of one of the two edges of the semiconductor region on an upper stream side of the projection direction is L 1 , and a width of the other of the two edges on a down stream side is L 2 , and a relation L 1 >L 2 is satisfied, in a condition that the one of the two edges and the other of the two edges are provided on the same semiconductor region formed as the substantially quadrangular doughnut ring; a first electrode selectively formed on an upper surface of the junction forming region; and a second electrode formed on the second main surface of the silicon carbide substrate, wherein L 0 is a depletion layer length at the maximum breakdown voltage, and relationships L 1 >3.0L 0 and L 2 >2.5L 0 are satisfied, where said L 0 has a relationship: L 0 =∈s*E BD /(e*Nd), where ∈s is a dielectric constant of the silicon carbide layer, E BD is an intensity of a breakdown electric field, e is an elementary electric charge, and Nd is a doping concentration of the silicon carbide layer.