A semiconductor device (110,120) comprising: a semiconductor layer of a first conductor type; a first semiconductor layer (23,33) of a second conductor type that is formed on the front side of the semiconductor layer; a second semiconductor layer (24,36) of the second conductor type that is selectively formed in a surface layer of the first semiconductor layer (23,33) and has a higher impurity concentration than the first semiconductor layer (23,33), wherein a third semiconductor layer (5, 34) of the second conductor type that is formed on the first semiconductor layer (23,33) and the second semiconductor layer (24,36) and has a lower impurity concentration than the second semiconductor layer (24,36); a first semiconductor region of the first conductor type that is formed in a surface layer of the third semiconductor layer (5, 34) that corresponds to the second semiconductor layer (24, 36); a second semiconductor region of the second conductor type, selectively formed in a surface layer of the first semiconductor region; an input electrode that contacts the second semiconductor region; a control electrode that is disposed above part of the first semiconductor region with an insulating film, the part being sandwiched between the second semiconductor region and the third semiconductor layer (5, 34) in a direction parallel to the surface of the first semiconductor region; and an output electrode that is disposed on the back side of the semiconductor layer, wherein the second semiconductor layer (24, 36) is only disposed under the first semiconductor region of the first conductor type with the third semiconductor layer (5, 34) of the second conductor type in-between, characterized in that the width of the second semiconductor layer (24, 36) in the horizontal direction is approximately identical to that of the first semiconductor region of the first conductor type. a semiconductor layer of a first conductor type; a first semiconductor layer (23,33) of a second conductor type that is formed on the front side of the semiconductor layer; a second semiconductor layer (24,36) of the second conductor type that is selectively formed in a surface layer of the first semiconductor layer (23,33) and has a higher impurity concentration than the first semiconductor layer (23,33), wherein a third semiconductor layer (5, 34) of the second conductor type that is formed on the first semiconductor layer (23,33) and the second semiconductor layer (24,36) and has a lower impurity concentration than the second semiconductor layer (24,36); a first semiconductor region of the first conductor type that is formed in a surface layer of the third semiconductor layer (5, 34) that corresponds to the second semiconductor layer (24, 36); a second semiconductor region of the second conductor type, selectively formed in a surface layer of the first semiconductor region; an input electrode that contacts the second semiconductor region; a control electrode that is disposed above part of the first semiconductor region with an insulating film, the part being sandwiched between the second semiconductor region and the third semiconductor layer (5, 34) in a direction parallel to the surface of the first semiconductor region; and an output electrode that is disposed on the back side of the semiconductor layer, wherein the second semiconductor layer (24, 36) is only disposed under the first semiconductor region of the first conductor type with the third semiconductor layer (5, 34) of the second conductor type in-between, characterized in that the width of the second semiconductor layer (24, 36) in the horizontal direction is approximately identical to that of the first semiconductor region of the first conductor type.