A semiconductor device includes a first semiconductor substrate of a first band-gap material and a second semiconductor substrate of a second band-gap material. The second band-gap material has a lower band-gap than the first band-gap material. A heterojunction is formed between the first semiconductor substrate and the second semiconductor substrate substantially in a first plane. The semiconductor device further includes, in a cross-section which is perpendicular to the first plane, a first semiconductor region of a first conductivity type and a second semiconductor region of the first conductivity type both of which extend from the second semiconductor substrate at least partially into the first semiconductor substrate. The first and second semiconductor regions are spaced in the first semiconductor substrate from each other in a direction parallel to the first plane by a first distance which is arranged in an area proximate to the heterojunction and which is larger than a second distance which is arranged in an area distal to the heterojunction.