The formation of partial AlGaN trench recess filled with multiple fluorinated gate dielectric layers as m etal-insulator-semiconductor (MIS) gate structure for GaN-based HEMT power devices is designed, fabricated and experimentally verified. The approach realizes the device normally-off operational mode and at the same time is able to preserve the good mobility in the 2DEG channel for a maximum on-state current. Experimental measurements on the fabricated MIS-HEMT devices indicate a high gate threshold voltage (V-th) at around 5 V and a very low gate leakage current at pA/mm level. This proposed gate structure provides very promising properties for GaN-based power semiconductor devices in future power electronics switching applications. (C) 2015 Elsevier Ltd. All rights reserved.