Method of making bipolar transistor

A method of manufacturing a bipolar transistor, comprising

• defining a collector region of semiconductor having a central region longitudinally between end regions;
• forming an insulating layer on the lateral sidewalls and top of the collector region in the central region;
• forming base contact regions on both lateral sides of the collector region in the central region;
• forming a gap between the tops of the base contact regions, the gap exposing the collector region in the central region;
• depositing a base semiconductor layer (2) on the exposed collector region in the gap, on the sidewalls of the gap and the tops of the polysilicon base contact region adjacent to the gap;
• forming spacers on the lateral inside edges of the base semiconductor layer in the gap;
• and
• filling the gap with an emitter semiconductor layer.