We demonstrate the first high-permittivity ceramic oxide for use as the gate oxide of the GaN-based metal-oxide-semiconductor (MOS) capacitor. An ilmenite magnesium titanate (MgTiO(3)) thin film prepared by sputtering was studied. When oxygen was introduced during sputtering, the preferred orientation changed from spinel Mg(2)TiO(4) (111) to ilmenite MgTiO(3) (003). The X-ray diffractometry theta-2 theta and -scans were performed to identify the preferred films. Possible epitaxial relationships at the Mg(2)TiO(4) (111)/GaN (001) and MgTiO(3) (003)/GaN (001) interfaces were proposed. Finally, the electrical properties of the Al/MgTiO(3) (003)/GaN (001)/Al MOS capacitor were presented.