This paper studies the effect of emitter width on the dc current gain, βF , and ac figures of merit, cut-off frequency, f T, and maximum oscillation frequency, f max, of realistic structures for 200 GHz SiGe heterojunction bipolar transistors (HBTs) using two-dimensional drift-diffusion (DD), hydrodynamic (HD) and energy balance (EB) simulations. The carrier transport models used are briefly presented. The SiGe-HBTs studied have a base thickness of 15 nm. Results of the three transport models are shown and analyzed, for the different emitter geometries.This paper studies the effect of emitter width on the dc current gain, βF , and ac figures of merit, cut-off frequency, f T, and maximum oscillation frequency, f max, of realistic structures for 200 GHz SiGe heterojunction bipolar transistors (HBTs) using two-dimensional drift-diffusion (DD), hydrodynamic (HD) and energy balance (EB) simulations. The carrier transport models used are briefly presented. The SiGe-HBTs studied have a base thickness of 15 nm. Results of the three transport models are shown and analyzed, for the different emitter geometries.