Silicon-Germanium (SiGe) technology effectively merges the desirable attributes of conventional silicon-based CMOS manufacturing (high integration levels, at high yield and low cost) with the extreme levels of transistor performance attainable in classical III-V heterojunction bipolar transistors (HBTs). SiGe technology joins together on-die high-speed bandgap-engineered SiGe HBTs with conventional Si CMOS to form SiGe BiCMOS technology, including all the requisite RF passive elements and multi-level thick-Al metalization required for high-speed circuit design. Such an silicon-based integrated circuit technology platform presents designers with an ideal division of labor for realizing optimal solutions to many performance-constrained mixed-signal (analog + digital + RF) systems. The unique bandgap-engineered features of SiGe HBTs enable several key merits with respect to operation across a wide variety of so-called “extreme environments”, potentially with little or no process modification, ultimately providing compelling advantages at the circuit and system level, across a wide class of envisioned commercial and defense applications. Here we give an overview of this interesting field, focusing primarily on the intersection of SiGe HBTs, and circuits built from them, with radiation-intense environments such as space.