Limited by increased parasitics and thermal effects as device size increases,current commercial SiGe power HBTs are difficult to operate at X-band (8~12GHz) frequencies with adequate power added efficiencies at high power levels.We find that,by changing the heterostructure and doping profile of SiGe HBTs,their power gain can be significantly improved without resorting to substantial lateral scaling.Furthermore,employing a common-base configuration with a proper doping profile instead of a common-emitter configuration improves the power gain characteristics of SiGe HBTs,thus permitting these devices to be efficiently operated at X-band frequencies.In this paper,we report the results of SiGe power HBTs and MMIC power amplifiers operating at 8~10GHz.At 10GHz,a 22.5dBm (178mW) RF output power with a concurrent gain of 7.32dB is measured at the peak power-added efficiency of 20.0%,and a maximum RF output power of 24.0dBm (250mW) is achieved from a 20 emitter finger SiGe power HBT.The demonstration of a single-stage X-band medium-power linear MMIC power amplifier is also realized at 8GHz.Employing a 10-emitter finger SiGe HBT and on-chip input and output matching passive components,a linear gain of 9.7dB,a maximum output power of 23.4dBm,and peak power added efficiency of 16% are achieved from the power amplifier.The MMIC exhibits very low distortion with 3 rd order intermodulation (IM) suppression C/I of-13dBc at an output power of 21.2dBm and over 20dBm 3 rd order output intercept point (OIP3). Limited by increased parasitics and thermal effects as device size increases, current commercial SiGe power HBTs are difficult to operate at X-band (8-12GHz) frequencies with adequate power added efficiencies at high power levels. We find that, by changing the heterostructure and doping profile of SiGe HBTs, their power gain can be significantly improved without resorting to substantial lateral scaling. Still further, employing a common-base configuration with a proper doping profile instead of a common-emitter configuration improves the power gain characteristics of SiGe HBTs, thus permitting these devices to be effectively operated at X-band frequencies.In this paper, we report the results of SiGe power HBTs and MMIC power amplifiers operating at 8 ~ 10GHz. At 10GHz, a 22.5dBm (178mW) RF output power with a concurrent gain of 7.32 dB is measured at the peak power-added efficiency of 20.0%, and a maximum RF output power of 24.0 dBm (250 mW) is achieved from a 20 emitter finger SiGe power HBT. demons tration of a single-stage X-band medium-power linear MMIC power amplifier is realized at 8GHz. Employing a 10-emitter finger SiGe HBT and on-chip input and output matching passive components, a linear gain of 9.7dB, a maximum output power of 23.4 dBm, and peak power added efficiency of 16% are achieved from the power amplifier. The MMIC exhibits very low distortion with 3 rd order intermodulation (IM) suppression C / I of -13 dBc at an output power of 21.2 dBm and over 20dBm 3 rd order output intercept point (OIP3).