A Reverse-conducting semiconductor device which comprises a freewheeling diode and an insulated gate bipolar transistor on a common wafer, part of which wafer forms a base layer of a first conductivity type with a first doping concentration and a base layer thickness. The insulated gate bipolar transistor comprises a collector side and an emitter side opposite the collector side of the wafer. A cathode layer of a first conductivity type with at least one first region and a anode layer of a second conductivity type with at least one second and pilot region are alternately arranged on the collector side. Each region has a region area with a region width surrounded by a region border. The Reverse-conducting-IGBT of the present application satisfies a number of specific geometrical rules.