This article presents an analytical and coherent design method for the generalized high-efficiency broadband parallel-circuit (PC) Class-E/F ₃ power amplifier (PA). By importing the initial phase shift of the third harmonic and adding series reactive element to the load network, a free design parameter can be defined and the design space of the load network parameters are expanded. The design equations of the idealized waveforms and the optimum values of the load network components are derived in detail, and the performance of the peak drain voltage, maximum operating frequency, and power output capability can be improved. In addition, with the expanding space of load network, the generalized PC Class-E/F ₃ structure exhibits broadband capability. A matching method with the real frequency technique (RFT) and the de-embedding technique is presented to design the optimal broadband matching network. To verify the validity of the proposed method, a broadband high-efficiency PA working from 1.7 to 2.6 GHz (fractional bandwidth of 42%) is designed. The experimental results of the fabricated PA present high-efficiency characteristics of 68.5%-81% drain efficiency and 62%-75.8% power-added efficiency with 38.8-40.5 dBm output power over the whole operation bandwidth.