This paper presents two CMOS power amplifiers which realize frequency band selection. Each PA consists of two stages and uses a transformer to obtain large output power with high efficiency. Furthermore, the capacitive cross-coupling at the second stage reduces a die area of the bypass capacitance. The proposed PAs are fabricated by a 0.18µm CMOS process. With a 3.3V supply, the PAs achieve a output 1-dB compression point of larger than 25dBm from 2.2GHz to 5.4GHz, maximum of peak power added efficiency (PAE_peak) are 30% and 27% for 2-band and 3-band PAs, respectively. The proposed PAs have advantages which are a band-selectable ability within a desired frequency range and a realization of CMOS PA with high power efficiency.