The total dose radiation effects on SiGe HBT and Si BJT were studied and then compared. It is shown that Ic changes slightly while Ib increases obviously with the increase of dose. Thus the degradation of β is dominated by the increasing Ib. The SiGe HBT maintained 77% of peak current gain after 10 kGy (Si), while Si BJT degraded to 55% of peak current gain. The results show that SiGe HBT has much better resistance to Gamma irradiation than Si BJT.