A semiconductor device manufacturing method comprising: a first step in which a first conductivity-type impurity is implanted in a first conductivity type drift layer on a second main surface of a semiconductor substrate which is a surface opposite to a first main surface of the semiconductor substrate so as to form a first impurity region on the semiconductor substrate wherein the first conductivity-type impurity is implanted in the second main surface by using multiple ion implantations of different acceleration energies; a second step in which a second conductivity-type impurity is implanted in the second main surface using the acceleration energy lower than the multiple ion implantations so as to form a second impurity region wherein the second impurity region is formed so that a non-implantation region in which the impurity is not implanted is left between the second impurity region and the first impurity region in the semiconductor substrate ; a heat treatment step in which heat treatment is applied to the semiconductor substrate so that a buffer layer is formed by the first conductivity-type impurity , and a collector layer is formed by the second conductivity-type impurity ; the heat-treatment is applied so that a non-diffusion region in which the first conductivity-type impurity and the second conductivity-type impurity do not diffuse is left between the buffer layer and the collector layer the non-diffusion region having the same impurity concentration as the drift layer, wherein the multiple ion implantations are performed so that the dosage of the first conductivity-type impurity becomes larger as going closer to the second main surface side , wherein the impurity concentration profile of the buffer layer has only a single peak; the method further comprises a step in which a collector electrode in contact with the collector layer is formed. a first step in which a first conductivity-type impurity is implanted in a first conductivity type drift layer on a second main surface of a semiconductor substrate which is a surface opposite to a first main surface of the semiconductor substrate so as to form a first impurity region on the semiconductor substrate wherein the first conductivity-type impurity is implanted in the second main surface by using multiple ion implantations of different acceleration energies; a second step in which a second conductivity-type impurity is implanted in the second main surface using the acceleration energy lower than the multiple ion implantations so as to form a second impurity region wherein the second impurity region is formed so that a non-implantation region in which the impurity is not implanted is left between the second impurity region and the first impurity region in the semiconductor substrate ; a heat treatment step in which heat treatment is applied to the semiconductor substrate so that a buffer layer is formed by the first conductivity-type impurity , and a collector layer is formed by the second conductivity-type impurity ; the heat-treatment is applied so that a non-diffusion region in which the first conductivity-type impurity and the second conductivity-type impurity do not diffuse is left between the buffer layer and the collector layer the non-diffusion region having the same impurity concentration as the drift layer, wherein the multiple ion implantations are performed so that the dosage of the first conductivity-type impurity becomes larger as going closer to the second main surface side , wherein the impurity concentration profile of the buffer layer has only a single peak; the method further comprises a step in which a collector electrode in contact with the collector layer is formed. <EOS>