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SiGe power HBTs integrated in SiGe BiCMOS are developed and characterized at 2.4 GHz for 802.11b and 5.8 GHz for 802.11a wireless LAN applications. Design considerations of ballast resistors for SiGe power HBTs at these two frequencies are investigated for both good thermal stability and high RF power performance. The investigations show that emitter ballast resistors or base ballast resistors should be judiciously used for SiGe power HBTs operating at different frequencies in order to extract the best RF performance from these devices. An RF output power of 30.8 dBm with PAE of 50.2 % at 2.4 GHz and an output power of 27.3 dBm with PAE of 23.6 % at 5.8 GHz are achieved from single discrete SiGe power HBTs with 0.4μm in emitter width, respectively. These highest performance results demonstrate the great power amplification potential of SiGe HBTs for 802.11 wireless LAN applications.