A　novel　post-oxidation　annealing　(POA)　process　with　supercritical　N2O　(SCN2O)　fluid　is　reported　to　be　highly　effective　in　improving　the　interface　properties　of　the　SiO2/4H-silicon　carbide　(SiC)　(0001)　systems.　After　SCN2O　POA,　the　interface　state　density　reduces　to　2.8　times　10{{11}}　eV-1cm-2,　which　is　about　3.5　times　lower　than　that　after　a　traditional　high-temperature　N2O　POA　process.　Meanwhile,　the　highest　oxide　critical　electric　field　shows　an　increase　of　18.19%　and　the　near-interfacial　oxide　traps　is　reduced　by　69.90%　compared　with　that　after　N2O　POA　process.　The　process　temperature　is　as　low　as　120　°C.　The　significantly　reduced　processing　temperature　avoids　additional　defect　generation　while　the　supercritical　state　provides　a　stronger　nitridation　effect.　SCN2O　annealing　is　a　promising　candidate　for　POA　process　toward　high-performance　SiC　power　metal-oxide-semiconductor　field　effect　transistors　(MOSFETs).　©　1963-2012　IEEE.