AbstractX-band performance, high temperature DC operation, and uniformity have been evaluated for 1 μm gate AlGaN/GaN HEMTs grown by RF atomic nitrogen plasma MBE. Deposition and fabrication were performed on 2-inch (0001) saphirre substrates to determine process uniformity. HEMTs with 300 μm total gate width and dual gate finger geometry have been fabricated with 650–700 cm2/V s mobility. Maximum frequency cut-offs on the order of of 8–10 were achieved. DC performance at room temperature was >500 mA/mm, and external transconductance was >70mS/mn. The transistors operated at test temperatures of 425°C.