Owing to the high density and high mobility of two-dimensional electron gas (2DEG) induced by strong spontaneous polarization and piezoelectric polarization effect, AlGaN/GaN Schottky barrier diodes (SBDs) with high output current density and low on-resistance have proved to be a promising candidate. Anode of GaN SBD is the core structure, which affects the device performance such as turn-on voltage, reverse current, on-resistance, and breakdown voltage. Therefore, idealized Schottky junction with low interface state density is very important in achieving high-performance GaN SBD. In this work, AlGaN/GaN SBD with low work-function metal W as anode is fabricated, and the post-anode-annealing (PAA) treatment is found to be effective in promoting the bonding reaction between anode metal and GaN in the anode region. Comparing with GaN SBDs without PAA treatment, the interface state density decreases from 9.48×10 ¹⁵eV ^–1·cm ^–2to 1.77×10 ¹³eV ^–1·cm ^–2after PAA treatment. The reverse leakage current is reduced by two orders, which ascribes to the idealized anode interface with low interface state density. Meanwhile, the influence of interface state on carriers in the forward conduction process is also suppressed, and the differential on-resistance of the fabricated GaN SBDs decreases from 17.05 Ω·mm to 12.57 Ω·mm. It is obvious that the PAA process proves to be an effective method to suppress the interface states density at M/S interface, thus significantly improving the performance of GaN SBD, which is the key technology in fabricating the high-performance GaN device.