Abstract: The layout design of a multi-finger power SiGe HBT with non-uniform finger spacing is proposed to improve the thermal stability. Compared with the traditional HBT with uniform finger spacing, both simulated and experimental results shown that the peak temperature and the non-uniformity of the temperature profile in the HBT with non-uniform finger spacing are improved markedly, which is ascribed to the increasing the spacing between fingers, and hence suppressing the heat flow from adjacent fingers to the center finger effectively. Furthermore, the thermal resistance is improved by 13.69% and the power level for thermal regression is increased by 22.8% compared with that of the uniform finger spacing device. Therefore, both simulation and experiment prove that the layout design of HBTs with non-uniform finger spacing is very useful for improving the thermal stability of power HBTs.