In this work, we propose a novel enhancement-mode GaN metal-oxide-semiconductor high electron mobility transistor (MOS-HEMT) with a 10 nm T-gate length and a high-k TiO₂ gate dielectric. The DC and RF characteristics of the proposed GaN MOS-HEMT structure are analyzed by using a TCAD Software. The device features are heavily doped (n++ GaN) source/drain regions for reducing the contact resistances and gate capacitances, which uplift the microwave characteristics of the MOS-HEMT. The enhancement-mode GaN MOS-HEMTs showed an outstanding performance with a threshold voltage of 1.07 V, maximum extrinsic transconductance of 1438 mS/mm, saturation current at V_GS = 2 V of 1.5 A/mm, maximum current of 2.55 A/mm, unity-gain cut-off frequency of 524 GHz, and with a record maximum oscillation frequency of 758 GHz. The power performance characterized at 10 GHz to give an output power of 29.6 dBm, a power gain of 24.2 dB, and a power-added efficiency of 43.1%. Undoubtedly, these results place the device at the forefront for high power and millimeter wave applications.