SiGe alloys have been successfully applied to a number of semiconductor devices, including bipolar heterojunction transistors, field effect transistors (FET's), and optoelectronic devices and structures. This review paper will first summarize the results obtained to-date in bipolar transistors, highlighting the design flexibility and the trade-offs offered by SiGe heterojunction technology and bandgap engineering, like junction field/capacitance control, liquid nitrogen operation and complementary processes. The leverage of this technology in high speed circuits will be discussed, including the record 75 GHz fr and 60 GHz fmax
heterojunction bipolar transistors, the achievement of sub-25 ps ECL ring oscillator delay, and the doubling of the mobility in p-MODFETs. The applications of this technology to optoelectronic devices, including detectors and waveguides, will also be reviewed, to extend the use of silicon technology to long wavelength communication technology and infrared imaging.