The AlN/GaN/AlN heterostructure is attractive for microwave and millimeter-wave power devices due to its thin top barrier, tight carrier confinement, and improved breakdown voltage. This work explores the large-signal RF performance of high-electron-mobility transistors on this heterostructure. Results are highlighted by record high on-current of 3.6 A/mm, and record maximum oscillation frequency (f max ) of 233 GHz. The load-pull power sweep at 10 GHz demonstrate a peak power added efficiency

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... PAE) of 22.7% with an associated gain (G T ) of 8.7 dB and output power (P out ) of 3 W/mm. When optimized for power, the peak P out of 3.3 W/mm has an associated PAE of 14.7% and G T of 3.2 dB. This first demonstration is encouraging for the mm-wave power potential of the AlN/GaN/AlN HEMT. INDEX TERMS GaN, AlN, output power, mm-wave, load-pull.