In this study, the effects of self-heating on the f(T) and f(max) frequencies have been investigated in NpN SiGe heterojunction bipolar transistors (HBTs) by two-dimensional numerical device modeling using a commercial simulator. The device studied was a single emitter stripe, double mesa configuration with self-aligned base contacts where a Gaussian distribution was assumed for the base's boron profile. Increases in the base transit time and the collector delay time due to degradation in the electron mobility and saturation velocity and an increase in the base-collector depletion layer width were found to degrade the f(T) while increased base resistance also contributed to the reduction in f(max). The onset of significant device self-heating and degradation in f(T) and f(max) were observed for collector current densities of 5 x 10(4) A/cm(2) for V-CE = 2 V. (c) 2005 Elsevier Ltd. All rights reserved.