A high-power, high-efficiency, 6-18GHz monolithic microwave integrated circuit (MMIC) power amplifier (PA) utilizing active load modulation is devised and evaluated in this document. The ultra-wideband (UWB) MMIC PA, manufactured in $\boldsymbol{0.20-\mu} \mathbf{m}$ gallium nitride (GaN) process, is intended not only with standard passive matching but also with an active methodology to identify the most appropriate impedances. The PA assessment findings indicated a power added efficiency (PAE) of 25% to 38% over 6–18 GHz with an average power gain of 21 dB and an output power greater than 44 dBm (25 W) at a drain voltage of 28V at 1ms pulse width with 10% duty cycle. The chip dimension is 4.7mm × 5.5 mm (25.85 mm 2 ).