An n-type buffer region 6 is arranged between an n− drift region 1 and a p-type collector region 7, and has a higher impurity concentration than n− drift region 1 Assuming that α represents the ratio (WTA/WTB) between WTA expressed as: WTA = 2 ⁢ ɛ s ⁢ ɛ 0 ⁢ V qNd and the thickness WTB of the drift region held between the base region and the buffer region, the ratio (DC/DB) of the net dose DC of the collector region with respect to the net dose DB of the buffer region is at least α. Thus, a semiconductor device capable of ensuring a proper margin of SCSOA resistance can be obtained.