This paper presents the design of a dual-band power amplifier operating at 2.4 GHz and 3.35 GHz. The proposed topology is based on the use of composite right/left-handed unit cells. A composite right/left-handed cell exhibits a dualband frequency response at an arbitrary pair of frequencies because of its phase characteristics. A power amplifier based on an enhancement mode pseudomorphic HEMT transistor is simulated and manufactured. The fabricated prototype leads to a dual-band amplification and is characterized in terms of measurements. A maximum drain efficiency of 65% and 52% is achieved for an output level of 28.7 dBm and 27.5 dBm at 2.4 GHz and 3.35 GHz, respectively. The presented approach can be applied for the design of dual-band matching networks for microwave circuits operating at two arbitrary frequencies.