The post deposition microwave plasma annealing (MPA) is developed to obtain high quality Al2O3/SiC gate stacks. By optimizing the plasma power, the in-terface state density is reduced by 1 order of magni-tude to 6 × 1011 cm-2eV-1, the breakdown electric field is increased, and the voltage shift is effectively sup-pressed. XPS results show the oxygen plasma enters the Al2O3 dielectric and fills the incomplete lattice during the MPA process, meanwhile, the interface has not been further oxidized.