The effects of displacement of a p-n junction from coincidence with a SiGe/Si heterojunction have been investigated using a simple analytical model. The phenomenon is of interest for understanding the degradation in the performance of npn SiGe/Si heterojunction bipolar transistors where SiGe is employed in the base when there is boron outdiffusion that produces p-n junction displacement at one or both of the emitter and collector-base junctions. This analysis describes the formation of parasitic barriers in the conduction band associated with this p-n junction displacement. The barrier is significantly larger for the heterojunction located on the p-side, but the barrier height is also a function of the Ge content, doping level and the magnitude of the displacement. Junction bias and high current density flow also modulate the barrier's height. The implication of p-n junction displacement on the formation of parasitic barriers at the emitter and collector junctions in SiGe transistors and their dependence on device operation are discussed. (C) 2002 Elsevier Science Ltd. All rights reserved.