Gallium nitride high-electron-mobility transistors (GaN HEMTs), featuring high frequency, high power density, and superior efficiency, have become core devices in next-generation power electronics. However, in practical operating environments such as DC-DC converters or half-bridge circuits, GaN devices are frequently subjected to surge current stresses of varying magnitudes and pulse widths. The resulting reliability concerns, characterized by parameter degradation or even catastrophic device failure, remain a critical bottleneck limiting the widespread adoption of GaN technology. In this work, the reliability of a commercial 650 V Schottky-type p-GaN gate GaN HEMTs under surge current stress in the third-quadrant operation was systematically investigated. The surge current capability and gate leakage evolution of the devices were experimentally characterized under surge pulse widths of 10 ms, 7 ms, and 5 ms. The results indicate that a reduction in surge pulse width significantly enhances the device's surge current capability (with a maximum improvement of approximately 18.3%) and mitigates the hysteresis phenomenon induced by self-heating effects. Specifically, the hysteresis time decreased from 1.27 ms under a 10 ms pulse width to 0.46 ms under a 5 ms pulse width. Furthermore, the shorter pulse width alleviates the gate leakage current degradation caused by surge stress, with an overall reduction in the leakage current increment compared to longer pulse width. Through multi-dimensional failure analysis using OBIRCH, FIB, TEM, and EDS, complemented by TCAD simulations, the failure mechanism under surge current stress was elucidated. The intense electric field leads to the degradation of the gate Schottky contact, triggering a sharp increase in gate current. At the peak failure surge current, the gate current density reaches as high as 6.43×107 A/cm2. Ultimately, the synergistic effect of the strong electric field and excessive gate current induces electromigration of the gate metal, resulting in the formation of distinct voids at the original metal site. This study, for the first time, elucidates the surge current endurance and gate leakage degradation behavior of Schottky-type p-GaN gate GaN HEMTs under third-quadrant operation with varying surge pulse widths, and discovered the failure mechanism associated with Schottky contact degradation–induced metal electromigration, providing valuable insights for the design and application of high-performance GaN power devices.