GaN metal oxide semiconductor diodes were demonstrated utilizing MgO as the gate oxide. MgO was grown at 100degreesC on metal oxide chemical vapor deposition grown n-GaN in a molecular beam epitaxy system using a Mg elemental source and an electron cyclotron resonance oxygen plasma. H3PO4-based wet-chemical etchant was used to remove MgO to expose the underlying n-GaN for ohmic metal deposition. Electron deposited Ti/Al/Pt/Au and Pt/Au were utilized as ohmic and gate metallization, respectively. An interface trap density of low-to-mid-10(11) eV(-1) cm 22 was obtained from temperature conductance-voltage measurements. Terman method was also used to estimate the interface trap density, and a slightly lower number was obtained as compared to the conductance method. Results from elevated temperature (up to 300degreesC) conductance measurements showed an interface state density roughly three times higher (6 x 10(11) eV(-1) cm(-2)) than at 25degreesC.