In this work, we report the ultra-high RF power performance of GaN HEMTs at X- and Ka-band achieved by AlGaN/GaN/AlN:Fe heterostructure. Without field-plate design, a record output power density (P out ) of 33.1 W/mm and a peak power added efficiency (PAE) of 62.9% at X-band were achieved when tuned for maximum power and PAE, respectively. In addition, the laterally scaled-down device delivers a maximum P out up to 14.4 W/mm at Ka-band. These excellent load-pull results, spanning a broad frequency range, demonstrate the potential of the AlGaN/GaN/AlN:Fe epitaxial structure as an attractive material platform for advancing GaN/SiC HEMTs in RF power amplifier applications.