The present disclosure relates to semiconductor structures and, more particularly, to a lateral bipolar transistor and methods of manufacture. The structure includes: an extrinsic base region within a semiconductor substrate material; a shallow trench isolation structure extending into the semiconductor substrate material and bounding the extrinsic base region; an emitter region adjacent to the shallow trench isolation structure and on a side of the extrinsic base region; and a collector region adjacent to the shallow trench isolation structure and on an opposing side of the extrinsic base region.