A CMOS common-gate (CG) combining power amplifier is introduced, which has a simple load impedance adaptor. The CG stage of a cascode amplifier consists of a main amplifier with a load impedance adapter and an auxiliary amplifier with a phase compensator, which are biased for classes AB and C, respectively. The proposed configuration not only increases the efficiency of the power amplifier (PA) at back-off powers, but also increases the linearity at high output powers by canceling AM-AM and AM-PM nonlinearities of the main amplifier with those of the auxiliary amplifier. A load impedance adaptor can be used to match two different optimum load impedances of the main and auxiliary amplifiers simultaneously. A phase compensator is introduced to match the output phases of both amplifiers. It has a die size of 0.9 x 1.63 mm(2) operates at 2.484 GHz with a 3.3 V supply, which is implemented with the 0.18-mu m CMOS technology. It shows a linear output power of 22.1 dBm with a PAE of 32% for an 802.11 n signal at error vector magnitude (EVMs) of -25 dB, and it also shows apparent efficiency improvements at back-off powers.