The effects of 1.25 MeV Co-60 gamma (gamma) irradiation on the dc electrical characteristics of self-aligned SiGe HBTs, and their post-stress reversibility have been studied. Compared with electrical (hot-carrier) stressing, radiation stress leads to qualitatively similar changes in the current gain of devices. However, there are some differences in the spatial distribution of the damage and details of the changes in the dc characteristics following radiation or hot-carrier stressing. This was confirmed by the inverse mode measurements. The radiation-induced degradation was stable at room temperature, and there was less recovery of the damage at elevated temperature compared with that for the electrically stressed devices. If the stressed devices were annealed for a long time further changes occurred, as often seen in accelerated lifetime testing Crown Copyright (C) 2004 Published by Elsevier Ltd. All rights reserved.