Abstract: An X-band power amplifier（PA）for T/R（transmit/receive）module of active phased array is presented. This PA is designed using cascade topology with linear two- stage single- ended structure. Input and output matching networks are integrated on a chip. A simple linearizer biasing circuit is achieved to reach high gain and linear output power. Based on 0.18 μm SiGe BiCMOS 7 WL process technology，the measurement results of the PA show that the small signal gain could reach up to 21.8 dB，and output 1 dB compression point is 10.4 dBm at 8.5 GHz of power supply 3.3 V. The amplifier is well-matched to deliver the maximum output power，and the total area is only 1.4 mm×0.8 mm，which realizes integration with the T/R chip.