Abstract: GaN semiconductor has received extensive attention from researchers due to its excellent physical properties. However, the development of the GaN-based HEMT technology for normally-off operation is still insufficient. This research focused on the thin-barrier normally-off HEMTs which can effectively reduce the etching damage in the gate trench, suggesting that it has great potential in the future power electronics market. In this research, a thin-barrier HEMT device based on SiON/Al₂O₃ stack dielectrics was fabricated. In the assistance of the dielectrics, the threshold voltage of the device is almost the same as that of the Schottky-gate device, which can achieve normally-off operation. The maximum off-state breakdown voltage can reach 700V and the gate voltage tolerance exceeds 23V. Besides, the threshold voltage shift is less than 1V during the positive gate stress test over 1000s. All the results indicate the advantages of the thin-barrier HEMT device.