A global additional uniaxial stress ranging from 1 GPa to 1 GPa along different directions has been applied to SiGe HBTs in order to improve the high-frequency performance of these devices. Two transistors have been investigated: a slow one (peak f(r) = 110 GHz) and a fast one (peak f(r) = 750 GHz). The results from full-band Monte Carlo simulations show that the cutoff frequency of both devices can be improved by more than 30 percent under suitable stress conditions. A spherical-harmonics-expansion simulator is also used to investigate the spatial origin of this improvement, where it is found that the transit times are reduced in all regions (base, collector, emitter). (C) 2011 Elsevier Ltd. All rights reserved.