Deep-level transient spectroscopy (DLTS) measurements have been performed on SiGe heterojunction bipolar transistors fabricated in a complementary metal–oxide–semiconductor compatible polysilicon self-aligned process. A detailed study of the emitter–base capacitance transient as a function of the filling pulse parameters and transistor geometry has shown that the deep levels are correlated to point defects uniformly distributed along the emitter–base junction periphery and attributed to the reactive ion etching (RIE) process. The observed deep electron traps are located at 0.6 eV below the conduction band with a capture cross section of10−17 cm2.In order to confirm that the observed defects were not correlated to the SiGe base material, a similar investigation was carried out on mesa devices grown in the same reactor with the same intrinsic structure but whose emitter–base active zone did not suffer RIE. In these devices, a new electron trap with an activation energy of 0.38 eV and a capture cross section of10−19 cm2is detected. This trap is sensitive to the electric field as in the case of the self-aligned structure, but a detailed study has shown that it has a different origin. Finally, the first peripheral electron trap atEc−0.6 eVis not observed in mesa devices in good agreement with our first hypothesis.