A fully integrated linear CMOS power amplifier (PA) for the broadband operation is developed for handset applications. This amplifier can handle a wideband signal. To achieve broadband/wideband operation, an analysis of the intermodulation distortion for the asymmetric source in a differential cascode structure is presented. Based on the analysis, the linearization technique using a second harmonic circuit at the gate of the common gate is proposed to reduce the asymmetry. The proposed PA with an on-chip transmission-line transformer, which has a broadband matching characteristic, is fabricated using a 0.18-μm RF CMOS technology. The measurement results show that the sideband asymmetry is less than 0.6 dB for a signal with up to 50-MHz bandwidth, and the peak average power is improved by 1.2 dB within the linearity spec of a 16-QAM 7.5-dB peak-to-average power ratio long-term evolution signal. The PA delivers a power-added efficiency of 36.5%-31.2% and an average output power of 27.5-27.1 dBm under an ACLR _E-UTRA of -30.5 dBc for a 50-MHz bandwidth signal across 1.4-2.0-GHz carrier frequency.