In this work, an energy band-modulated self-aligned p-AlGaN/u-GaN MESFET with a tungsten (W) gate is demonstrated. A high

$\textit{I}_{\text{ON}}$

$\textit{I}_{\text{OFF}}$

of 2

$\times$

$^{\text{7}}$

, a low subthreshold swing (SS) of 90 mV/dec, and an enhancement-mode threshold voltage (

$\textit{V}_{\text{TH}})$

$-$

0.3 V are obtained. Benefiting from the TMAH-treated etching surface and the post gate annealing-treated Schottky interface, an extremely low trap state density of 2.8–4.8

$\times$

$^{\text{11}}$

$^{-\text{2}}\cdot$

$^{-\text{1}}$

was confirmed by the conductance method. The dual-sweep transfer I – V curves show negligible hysteresis and coincide well even after a harsh long-term OFF-state stress. In addition, the breakdown voltage of the fabricated E-mode p-AlGaN/u-GaN composite-channel MESFET with a gate-to-drain length (

$\textit{L}_{\text{GD}})$

of 4

$\mu $

m reaches

$-$

365 V. The breakdown field reaches approximately 0.9 MV/cm, and the differential ON-resistance is 2.8 k

$\Omega\cdot$

mm.