A semiconductor device includes transistor cells formed along a first surface at a front side of a semiconductor body in a transistor cell area. A drift zone structure forms first pn junctions with body zones of the transistor cells. An auxiliary structure between the drift zone structure and a second surface at a rear side of the semiconductor body includes a first portion that contains deep level dopants requiring at least 150 meV to ionize. A collector structure directly adjoins the auxiliary structure. An injection efficiency of minority carriers from the collector structure into the drift zone structure varies along a direction parallel to the first surface at least in the transistor cell area.