A compact fully integrated power amplifier for mobile devices based on the SiGe BiCMOS process is proposed. The design uses a cascode driver stage cascaded with a common emitter power stage to increase the power gain of the amplifier， integrates a CMOS power supply on-chip to provide bias current， and uses distributed ballast resistors and a bias circuit with thermal negative feedback effect to compensate the junction temperature so as to prevent amplifier failure at high-temperature operation. A compact circuit-level thermal coupling model is used to simulate and verify the proposed thermal stabilization measures. The post-simulation results show that PA has an output gain of 32.5 dB in the working range of 2.4~2.5 GHz under a 3.3 V power supply， S11&S22<-10 dB， and the output power at the 1 dB compression point is 25.4 dBm. The maximum junction temperature is less than 65 ℃ （saturation）. The chip area is only 1.25×0.76 mm2. The test results show that in the working environment of -45~ 85 ℃， the amplifier can work well in the application where the gain requirement is 26.5~ 32.9 dB. The output power at the 1 dB compression point is 24.3 dBm. Using a 20 MHz 64-QAM OFDM modulation signal test， the output power of DEVM reaching -30 dB is 18.1 dBm.