Metal-insulator-semiconductor (MIS) capacitors have been fabricated on n-type GaN (0001) films using thermally grown Ga2O3, remote plasma enhanced chemical vapor deposited (RPECVD) SiO2, and molecular beam epitaxy (MBE) AIN as the gate insulator and Al as the gate electrode. Each GaN epitaxial layer was grown by organometallic chemical vapor deposition (OMCVD) on a 6H-SiC(0001) substrate on which was previously deposited a 1000Å buffer layer of AIN. Nitrogen-free polycrystalline films of Ga2O3 were grown on the GaN. Capacitancevoltage measurements of capacitors fabricated from this oxide showed distinct depletion and accumulation regions with significant leakage. The AIN and SiO2 capacitors demonstrated better electrical characteristics than the Ga2O3 because of lower leakage. The RPECVD SiO2/GaN heterostructures, in particular, showed good agreement with the curves calculated for an ideal oxide and a small amount of hysteresis.