A power amplifier using the common-gate (CG)/common-source (CS) circuit topology to implement the linearity improvement technique has been designed and implemented in 0.15 μm GaAs pHEMT technique for WLAN/WiMAX applications. The simulation analysis reveals that the CG circuit provides the characteristics of gain and phase compensation to improve the nonlinearity of CS circuit. Combining the CG circuit with CS amplifier can achieve the low signal distortion without consuming dc power and losing the signal gain, while operating at high output power. The power amplifier including the on-chip input/output matching networks is performed in Class-AB operation with a quiescent current of 320 mA and a linear gain of 16 dB under a 5.5 V dc supply. The amplifier also exhibits the power performances of the 1-dB compression point and the saturation power are 27.5 dBm and 29.5 dBm, containing the maximum power-added efficiency (PAE) up to 25 %. With the two-tone intermodulation distortion (IMD) testing, the measured IMD3 is close to -35 dBc under an output power of 25 dBm.