In modern communication systems, the use of multiband approach, where the frequency bands can be selectable, is highly desired to achieve the highest wireless data rate and can also reduce transceiver complexity, size, and cost. This article presents, for the first time, a fully integrated band-switchable CMOS power amplifier (PA) utilizing a pioneering approach toward switching impedance matching networks. In the proposed approach, which is called bit optimized reconfigurable network (BORN), an $n$ -bit BORN may create ( $2^{n} -1$ ) number of switchable frequency bands utilizing only one active block and only $n$ -number of impedance matching network arms controlled by applying digital bits to switches. As a proof of concept, a 2-bit BORN PA is designed and fabricated in a 0.18- $\mu \text{m}$ CMOS process with a die size of 3.1 mm $\times1.6$ mm, which covers three bands of interest by utilizing only two input/output matching networks. The proposed 2-bit BORN PA delivers the saturated output power ( $P_{\mathrm {sat}}$ ) of 21.3/22.3/23.0 dBm, the output 1-dB compression point ( $P_{\mathrm {1\,dB}}$ ) of 19.5/20.0/21.0 dBm, and the 3-dB bandwidth of 400/425/550 MHz at the three targeted frequency bands, respectively. The measured results show promising improvement with respect to the state of the art.