Surface　treatment　is　quite　vital　to　reduce　the　reverse　leakage　current　and　improve　the　current　On-Off　ratio　of　gallium　nitride　(GaN)　quasi-vertical　Schottky　barrier　diode　(SBD).　In　this　work,　we　report　a　new　nondestructive　low　temperature　supercritical　CO2　fluid　(SCF)　nitridation　technology　to　treat　the　surface　of　GaN　and　substantially　reduce　the　leakage　current　of　GaN　quasi-vertical　SBD.　The　X-ray　photoelectron　spectroscopy　(XPS)　reveals　the　increased　nitriding　degree　and　oxygen　doping　degree　in　the　form　of　GaOx　after　the　SCF　process　results　in　the　leakage　performance　improvement.　As　a　result,　the　defects　at　metal/semiconductor　interface　are　passivated.　Also,　because　of　NH-2　and　OH-　generated　from　the　SCF　process,　the　surface　peak　electric　field　of　n-GaN　decreases,　and　thus　the　breakdown　voltage　is　enhanced.　The　reverse　leakage　current　density　is　reduced　by　more　than　three　orders　of　magnitude　from　3.7　×　10-6　to　3.52　×　10-9　A/cm2　(at　-3　V)　and　the　ON-/　OFF-current　ratio　is　improved　by　three　orders　from　8　×　107　to　5.74　×　1010.　©　2020　IEEE.