Third generation 200 GHz silicon-germanium Heterojunction Bipolar Transistors (Si-Ge HBTs) were irradiated with high dose Co-60 gamma radiation up to 100 Mrad Pre-radiation and post-radiation DC figures of merits were used to quantify the radiation tolerance of the different geometry devices The different electrical characteristics like Gummel measurements excess base current current gain trans-conductance neutral base recombination avalanche multiplication of carriers and output characteristics were studied for different doses from 100 krad to 100 Mrad of total doses The Si-Ge HBTs showed robust ionizing radiation tolerance up to a total dose of 100 Mrad (C) 2010 Elsevier Ltd All rights reserved