A dual-mode CMOS power amplifier (PA) with an integrated tunable matching network is presented. A switched capacitor is fully analyzed to implement a tunable matching network in terms of power-handling capability, tuning ratio, quality factor, and linearity. Based on the presented consideration, a 3.3-V 2.4-GHz fully integrated CMOS dual-mode PA is implemented in a 0.18-μm CMOS process. The PA has two power modes, high-power and low-power (LP), and each mode is optimally matched by the tunable matching network. The LP mode enables more than 50% dc current reduction from 0- to 10-dBm power range. The improved efficiency in this study is approximately twice that of other multimode CMOS PAs reported thus far.