High κ Ga 2 O 3 (Gd 2 O 3 ) dielectric was deposited on n-type GaN (0001) using molecular beam epitaxy (MBE). TiN/Ga 2 O 3 (Gd 2 O 3 )/GaN metal–oxide–semiconductor (MOS) diodes have exhibited a negligible frequency dispersion, low leakage currents (∼10 −8 A/cm 2 ), and a low interfacial density of states (D it ) of 10 11 cm −2 eV −1 at the midgap. Well-behaved capacitance–voltage (CV) curves with accumulation and depletion behaviors were shown, with a dielectric constant of 14.7. Forming gas annealing at 600°C has reduced the frequency dispersion in the CV curves. A sharp oxide/semiconductor interface was shown by high-resolution transmission electron microscopy (HR-TEM).