In this brief, a thorough investigation is performed to analyze the effect of ionizing radiation and temperature on SiGe HBT. The effect of 1 Mrad (Si) gamma total dose is analyzed on device performance parameters: base transit time, cut-off frequency, and maximum oscillation frequency. Also, the effects of both intrinsic and extrinsic reliability issues i.e., radiation rich environment, temperature, and self heating are analyzed on SiGe HBT and SiGe BiCMOS HBT using TCAD.