In the last few years Si/SiGe/Si heterostructures grown by molecular beam epitaxy (MBE) with its high precision and reproducibility have been used to build high-frequency and low-noise heterojunction bipolar transistors (HBTs). The latest optimization of layer design led to a SiGe HBT with an f(max) value of 160 GHz. As a circuit demonstrator a DC-IS GHz low power wideband amplifier was integrated showing a gain of 9.5 dB at only 18 mW power consumption. Several monolithically integrated 26 GHz and 40 GHz VCOs were fabricated on high-resistivity substrates using SiGe HBTs and on-chip varactors built from the same MBE layers. A multi-finger power HBT exhibited 100 mW at 5.7 GHz in a hybrid class A amplifier with 30% efficiency. At 2 GHz, I W output power was obtained with 44% power-added efficiency. Mesa-type research transistors as well as fully passivated devices will be compared. A high-quality oxide passivation results in excellent low-frequency noise performance of SiGe HBTs with corner frequencies down to 300 Hz, At the same time the high-frequency noise is kept low due to the small base resistance leading to a measured noise figure of 0.5 dB at I GHz. In future a large number of circuit applications, in particular for mobile communications will profit From the high performance of SiGe HBTs.