This work presents a high power gain fully integrated 2.45 GHz CMOS differential power amplifier (PA) in a standard 0.18 μm CMOS process. The PA is implemented on a single chip, requiring no external baluns, matching or tuning networks. The circuit exploits injection locking method to achieve 40 dB power gain with a single stage amplifier, ensuring a power-added efficiency (PAE) of 32%. This PA brings the advantage of no driver stage in the input signal path. Moreover, if a higher output power is required, this PA becomes a driver stage best candidate due to its high gain. We prove that an injection locking PA can be the best candidate to a non-constant envelope PA driver, although we do not use a latest technique or topology to prove it. The maximum output power of 20.5 dBm, with a peak PAE of 36% occurs at 0 dBm input power level.