The enhancement mode n-channel GaN-based MOSFETs on Si substrates have been demonstrated. We achieved a low interface state density between SiO 2 and GaN, a high breakdown field, and a high reliability of SiO 2 by annealing after SiO 2 deposition on GaN. The SiO 2 was applied for the gate oxide of GaN MOSFET. The fabricated GaN MOSFETs using an ion implantation technique showed good normally-off operation with threshold voltage of 2.7 V, the maximum output current of over 3.5 A, and a high-temperature operation up to 300°C Furthermore, AlGaN/GaN hybrid MOS-HFETs were fabricated. The MOS-HFET has the merits of both a MOS channel and an AlGaN/GaN heterostructure with high mobility two dimensional electron gases. The maximum drain current of over 100 A was performed. The specific on-state resistance was 9.3 mΩ-cm 2. The fabricated device also exhibited good normally-off operation and the breakdown voltage of over 600 V.