This letter proposes a highly efficient CMOS linear power amplifier (PA) with cascode-cascade configuration. The proposed configuration improves AM-PM distortion through a capacitance variation compensation of the input capacitance of a common-gate stage in the main amplifier and a common-source stage of an auxiliary amplifier. In addition, the current consumption in the low-power region is significantly reduced structurally because the auxiliary amplifier is turned off. The PA is implemented in 0.18-mu m CMOS process with an output combining network in printed circuit board. It provides an average power of 24.5 dBm with a PAE of 45.6% for a long-term-evolution 10-MHz up-link signal with the ACLR(E)-UTRA of -30 dBc at 2 GHz.