A fully integrated differential class-AB power amplifier has been designed in a 0.25um CMOS technology. It is intended for medium output power ranges such as Bluetooth class I, and has an operating frequency of 2.45GHz. By using two parallel output stages that can be switched on or off, a high efficiency can be achieved for both high and low output power levels. The simulated maximum output power is 22.7 dBm, while the maximum power- added efficiency is 22%.