Mixed mode circuit and device simulation has been used to investigate the linearity properties-harmonic distortion of high-speed low voltage SiGe heterojunction bipolar transistors (HBTs). The simulation test-circuit included the active device, modeled by finite element simulation, as well as passive elements in a SPICE circuit for DC-feed and AC-coupling of the RF-signal. Different Ge-profiles for reduced harmonic distortion have been investigated and compared to a conventional high-speed graded Ge-profile. To find an optimized Ge-profile for RF-applications other figure-of-merits, such as maximum cut-off frequency and minimum noise figure were also simulated. Using the same mixed mode simulation approach the design of the epitaxial collector doping profile for high breakdown voltage, high cut-off frequency and reduced harmonic distortion was investigated. (C) 2002 Elsevier Science Ltd. All rights reserved.