The strong spontaneous and piezoelectric polarizations in pseudomorphic AlGaN/GaN on SiC substrates are used to induce 2DEG sheet density of > 1 x 10 13 /cm 2 with mobility up to 1,700 cm 2 /vs. The processing sequence and HEMT electrode layout are presented. The output power and power-added efficiency in the 8-10 GHz frequency range are shown for CW bias conditions and optimum tuning in class B operation. Single-gate, center-fed 100 µm periphery devices gave 11.2 W/mm at 32% power-added efficiency; two-gate, 200 µm periphery devices with 50 µm pitch gave 8.7 W/mm at 48% power-added efficiency, and 12-gate, 1.5 mm periphery devices with 50 µm pitch gave 6.7 W/mm at 42% power-added efficiency. For comparison, the latter gave 9.4 W/mm at 43% power-added efficiency in low duty cycle pulsed operation . The key limitation for CW power performance is self-heating, which raises the knee voltage by (T/300) 1.8 for T channel temperature in °K.