In this work, enhancement-mode (E-mode) AlGaN/GaN metal–insulator–semiconductor high-electron-mobility transistors (MIS-HEMTs) with high-κ LaLuO₃ (LLO) gate dielectric were fabricated by deploying the CF₄ plasma treatment technique in a gate-dielectric-first planar process. CF₄ plasma treatment can shift the threshold voltage from -2.3 V [for depletion-mode (D-mode) LLO MIS-HEMTs] to 0.6 V (for E-mode LLO MIS-HEMTs). Transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) results suggest that fluorine ions could penetrate through the polycrystalline/amorphous LLO film and be implanted into the (Al)GaN barrier layer. The primary threshold voltage (V _TH) shift mechanism of the E-mode LLO MIS-HEMTs is the negatively-charged fluorine ions in (Al)GaN, while fluorine atoms form chemical bonds with La/Lu atoms in the fluorinated LLO film. The E-mode LLO MIS-HEMTs exhibit a drive drain current density of 352 mA/mm at V _GS = 2.5 V and a peak transconductance (G _m) of ∼193 mS/mm. Significant suppression of current collapse and low dynamic ON-resistance are obtained in the E-mode LLO MIS-HEMTs under high-drain-bias switching conditions.