A semiconductor device comprising: a semiconductor layer of a first conductor type; a first semiconductor layer of a second conductor type that is formed on the front side of the semiconductor layer ; a second semiconductor layer of the second conductor type that is selectively formed in a surface layer of the first semiconductor layer and has a higher impurity concentration than the first semiconductor layer , wherein a third semiconductor layer of the second conductor type that is formed on the first semiconductor layer and the second semiconductor layer and has a lower impurity concentration than the second semiconductor layer ; a first semiconductor region of the first conductor type that is formed in a surface layer of the third semiconductor layer that corresponds to the second semiconductor layer ; 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 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 is only disposed under the first semiconductor region of the first conductor type with the third semiconductor layer of the second conductor type in-between, characterized in that the width of the second semiconductor layer 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 of a second conductor type that is formed on the front side of the semiconductor layer ; a second semiconductor layer of the second conductor type that is selectively formed in a surface layer of the first semiconductor layer and has a higher impurity concentration than the first semiconductor layer , wherein a third semiconductor layer of the second conductor type that is formed on the first semiconductor layer and the second semiconductor layer and has a lower impurity concentration than the second semiconductor layer ; a first semiconductor region of the first conductor type that is formed in a surface layer of the third semiconductor layer that corresponds to the second semiconductor layer ; 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 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 is only disposed under the first semiconductor region of the first conductor type with the third semiconductor layer of the second conductor type in-between, characterized in that the width of the second semiconductor layer in the horizontal direction is approximately identical to that of the first semiconductor region of the first conductor type. <EOS>