The design of a 0.7~3.8GHz CMOS power amplifier (PA) for multi-band applications in TSMC 0.18-μm CMOS technology is presented. The PA proposed in this paper uses lossy matching network and low Q multistage impedance matching network to improve wideband. To achieve maximum linearity, this PA operates in the Class-A regime. The post-layout simulation results show that the power amplifier achieves 21.9dB of power gain, 22.3dBm of 1dB compression power output at 2GHz. The power adder efficiency (PAE) at gain compression point is 17.8% at 2GHz.