Abstract: A semiconductor device, comprising a substrate layer made of a semiconductor material of a first conductivity type and having a first insulation region, and a vertical bipolar transistor having a first vertical portion of a collector made of monocrystalline semiconductor material of a second conductivity type and disposed in an opening of the first insulation region, a second insulation region lying partly on the first vertical portion of the collector and partly on the first insulation region and having an opening in the region of the collector, in which opening a second vertical portion of the collector made of monocrystalline material is disposed, said portion including an inner region of the second conductivity type, a base made of monocrystalline semiconductor material of the first conductivity type, a base connection region surrounding the base in the lateral direction, a T-shaped emitter made of semiconductor material of the second conductivity type and overlapping the base connection region, wherein t