A method for manufacturing a bipolar punch-through semiconductor device is disclosed, which includes providing a wafer having a first and a second side, wherein on the first side a high-doped layer of the first conductivity type having constant high doping concentration is arranged; epitaxially growing a low-doped layer of the first conductivity type on the first side; performing a diffusion step by which a diffused inter-space region is created at the inter-space of the layers; creating at least one layer of the second conductivity type on the first side; and reducing the wafer thickness within the high-doped layer on the second side so that a buffer layer is created, which can include the inter-space region and the remaining part of the high-doped layer, wherein the doping profile of the buffer layer decreases steadily from the doping concentration of the high-doped region to the doping concentration of the drift layer.