This brief presents a high-efficiency inverse Class-F (Class-F-1) monolithic microwave integrated circuit (MMIC) power amplifier (PA) fabricated with 0.25-lm GaN-on-Si technology. The design is based on a compact output matching network (COMN), which consists of a harmonic control circuit (HCC), an L-section matching circuit and a bias line. In order to reduce the circuit area that make it suitable for monolithic integration, the HCC uses only three transmission lines to achieve the second and third harmonic control. In addition, the conventional quarter-wave bias line is replaced with a shorter, proper one. The proposed COMN simplifies the matching network while realizing Class-F-1 operation, which improves efficiency, output power and reduce chip size. The maximum power added efficiency of 64.5% is achieved at 3.0 GHz, with an output power of 38.4 dBm and a power gain of 10.3 dB.