The semiconductor device includes a p-type substrate (1) with an n-type epitaxial layer (5). Between the substrate and the epitaxial layer is an n-type buried layer (2). A p-type buried layer (4) in the initial buried layer forms a collector. An n-type trench region (20) forms the base in a part of the epitaxial layer and it has a higher doping concentration than the latter.The collector electrode is formed by an p-type diffusion region (6) on the p-type buried layer. In the trench region is formed a p-type diffusion region (7) as the transistor emitter. The trench region is in contact with the buried layer and with the diffusion region. Through the epitaxial layer the trench region is surrounded with a predetermined distance in the transistor vertical direction. The distance is such that a desired CB-transition breakthrough voltage is dependent on the upper surface doping concentration of the p-type diffusion region.
