4H-SiC(0001) MOSFET annealed in N2O at below 1150 degrees C is systematically investigated. Inversion-type planar MOSFETs show higher channel mobility and lower threshold voltage by increasing anneal temperature. Through C-V measurement of n-type MOS capacitors, the interface state density is revealed to decrease at higher anneal temperature. The field effect mobility of 30 cm(2)/Vs is achieved by 1150 degrees C anneal for 3 h, which is about 10 times higher than that of not annealed MOSFET. Epitaxial n-channel MOSFET annealed in N2O has been also fabricated. A positive threshold voltage of 0.46 V and the field effect mobility of 45 cm(2)/Vs are attained. The effective mobility at 2.5 MV/cm is 34 cm(2)/Vs, which is five times higher than that for not annealed sample, suggesting that the N2O anneal improves the MOS interface quality. (c) 2005 Elsevier Ltd. All rights reserved.