In this paper, a class AB power amplifier is proposed. The amplifier is designed for the 400MHz-440MHz single-chip wireless transceiver based on 0.18μm standard CMOS technology. The output power delivered by the amplifier could be digitally programmed at one of the following data: 10dBm, 5dBm, 0dBm and -5dBm. Its output 1dB compression point is better than 9dBm.