Multi-finger power SiGe heterojunction bipolar transistors (HBTs) with emitter ballasting resistor and non-uniform finger spacing are fabricated, and temperature profiles of them are measured. Experimental results show that both of them could improve the temperature profile compared with an HBT which has uniform finger spacing. For the HBT with emitter ballasting resistor, the ability to lower the peak temperature is weakened as power increases. However, for the HBT with non-uniform finger spacing, the ability to improve temperature profile is kept over a wide biasing range. Therefore, the experimental results directly prove that the technique of non-uniform finger spacing is a better method for enhancing the thermal stability of power HBTs over a wide biasing range. (c) 2007 Elsevier Ltd. All rights reserved.