A semiconductor device comprising: an active region comprising a second-conductivity-type diffusion region having a rectangular plane pattern which is arranged in a surface layer of one main surface of a first-conductivity-type semiconductor substrate; a metal electrode in ohmic contact with a surface of a central portion of said second-conductivity-type diffusion region; and a ring-shaped peripheral portion which surrounds the active region and includes an insulating film (3, 3a) on a surface thereof, wherein the peripheral portion includes a diffused second-conductivity-type diffusion region extension portion; a ring-shaped voltage-resistant region (1-1; 40) which surrounds the ring-shaped peripheral portion, characterized in that the second-conductivity-type diffusion region extension portion of the ring-shaped peripheral portion includes a plurality of second-conductivity-type stretch-out portions which are in direct contact with the second-conductivity-type diffusion region and are stretched out from an inner circumferential end of the ring-shaped peripheral portion toward an outer circumferential end of the ring-shaped peripheral portion in a stripe shape; and in that in the ring-shaped peripheral portion a plurality of first-conductivity-type surface portions of the substrate and the plurality of second-conductivity-type stretch-out portions are alternately arranged in the ring direction along the circumference of the active region to constitute a ladder-shaped extension portion, said surface portions of the substrate extending from said inner circumferential end toward said outer circumferential end in a stripe shape, the ring-shaped peripheral portion further including a ring-shaped second-conductivity-type diffusion region which surrounds the ladder-shaped extension portion, is in contact with the outer circumference sides of the second-conductivity-type stretch-out portions and has a diffusion depth larger than that of the second-conductivity-type stretch-out portions. an active region comprising a second-conductivity-type diffusion region having a rectangular plane pattern which is arranged in a surface layer of one main surface of a first-conductivity-type semiconductor substrate; a metal electrode in ohmic contact with a surface of a central portion of said second-conductivity-type diffusion region; and a ring-shaped peripheral portion which surrounds the active region and includes an insulating film (3, 3a) on a surface thereof, wherein the peripheral portion includes a diffused second-conductivity-type diffusion region extension portion; a ring-shaped voltage-resistant region (1-1; 40) which surrounds the ring-shaped peripheral portion, characterized in that the second-conductivity-type diffusion region extension portion of the ring-shaped peripheral portion includes a plurality of second-conductivity-type stretch-out portions which are in direct contact with the second-conductivity-type diffusion region and are stretched out from an inner circumferential end of the ring-shaped peripheral portion toward an outer circumferential end of the ring-shaped peripheral portion in a stripe shape; and in that in the ring-shaped peripheral portion a plurality of first-conductivity-type surface portions of the substrate and the plurality of second-conductivity-type stretch-out portions are alternately arranged in the ring direction along the circumference of the active region to constitute a ladder-shaped extension portion,