A radio-frequency magnetron sputtering technique and subsequent rapid thermal annealing (RTA) at 600, 700, 800, and 900 °C were implemented to grow high-quality Ga-doped Mg
O (GMZO) epi-layers. The GMZO films were deposited using a radio-frequency magnetron sputtering system and a 4 inch ZnO/MgO/Ga
(75/20/5 wt %) target. The Hall results, X-ray diffraction (XRD), and transmittance were determined and are reported in this paper. The Hall results indicated that the increase in mobility was likely caused by the improved crystallization in the GMZO films after thermal annealing. The XRD results revealed that Mg
O (111) and MgO
(200) peaks were obtained in the GMZO films. The absorption edges of the as-grown and annealed GMZO films shifted toward the short wavelength of 373 ran at a transmittance of 90%. According to these results, GMZO films are feasible for forming transparent contact layers for near-ultraviolet light-emitting diodes.