Disclosed is a semiconductor structure including a lateral heterojunction bipolar transistor (HBT). The structure includes a substrate (e.g., a silicon substrate), an insulator layer on the substrate, and a semiconductor layer (e.g., a silicon germanium layer) on the insulator layer. The structure includes a lateral HBT with three terminals including a collector, an emitter, and a base, which is positioned laterally between the collector and the emitter and which can include a silicon germanium intrinsic base region for improved performance. Additionally, the collector and/or the emitter includes: a first region, which is epitaxially grown within a trench that extends through the semiconductor layer and the insulator layer to the substrate; and a second region, which is epitaxially grown on the first region. The connection(s) of the collector and/or the emitter to the substrate effectively form thermal exit path(s) and minimize self-heating. Also disclosed is a method for forming the structure.