In this brief, a high-performance quasi-vertical GaN Schottky barrier diode (SBD) on sapphire substrate with post-mesa nitridation process is reported, featuring a low damaged sidewall with extremely low leakage current. The fabricated SBD with a drift layer of 1 μm has achieved a very high ON/OFF current ratio (Iscriptscriptstyle ON/Iscriptscriptstyle OFF of 1012 with a low leakage current of ∼ 10-9 A/cm2@-10 V, high forward current density of 5.2 kA/cm2 at 3 V in dc, a low differential specific ON-resistance (Rscriptscriptstyle ONsp) of 0.3 m Ω cm2, and ideality factor of 1.04. In addition, a transmission-line-pulse (TLP) I-V test was carried out and 53 kA/cm2 at 30 V in pulsed measurement was obtained without device failure, exhibiting a great potential for high power applications.