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In this letter, enhancement-mode AlGaN/GaN metal-oxide semiconductor high-electron-mobility transistors (HEMT) (MOS-HEMTs) are realized by using N2O plasma oxidation and Gd2O3 stacked-gate dielectric technologies. Before the gate metal was deposited, the AlGaN barrier layer was treated by 150-W N2O plasma for 200 s to remove the AlGaN native oxide layer and, simultaneously, to form Al2O3/ Ga2O3 compound insulator. Then, a 10-nm-thick high-dielectric-constant Gd2O3 thin film was electron-beam evaporated as a stacked-gate dielectric. To elucidate the interface phenomena of the device, the dependence of the 1/f noise spectra on the gate bias was studied. The fluctuation that is caused by trapping/detrapping of free channel carriers near the gate interface can be reduced by N2O plasma treatment. Additionally, the variation of the Hooge factor (αH) of a traditional metal gate GaN HEMT, measured at 77 K and 300 K, is huge, particularly in the subthreshold gate voltage regime. The tunneling leakage current that is induced by the interface traps is determined to be higher than that in the MOS-HEMT design. The threshold voltage (Vth) of depletion-mode GaN HEMT was -3.15 V, and this value can be shifted to +0.6 using N2O-treated stacked-gate AlGaN/GaN MOS-HEMTs.