A transformer-based high-order output matching network is proposed for broadband power amplifier design, which provides optimum load impedance for maximum output power within a wide operating frequency range. A design methodology to convert a canonical bandpass network to the proposed matching configuration is also presented in detail. As a design example, a push-pull deep class-AB PA is implemented with a third-order output network in a standard 90 nm CMOS process. The leakage inductances of the on-chip 2:1 transformer are absorbed into the output matching to realize the third-order network with only two inductor footprints for area conservation. The amplifier achieves a 3 dB bandwidth from 5.2 to 13 GHz with