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The low-temperature gate reliability of Schottky-type p-GaN gate AlGaN/GaN heterojunction field-effect transistors under forward gate voltage stress is investigated. Both temperature-accelerated and voltage-accelerated time-dependent gate breakdown stress experiments are performed. The p-GaN gate exhibits a shorter time-to-failure at a lower temperature. It is found that the time-to-failure at "use conditions" predicted by acceleration tests at high gate bias stress could be overestimated at low temperatures. Such a discrepancy stems from the distinct dominant gate leakage mechanisms at high/low gate bias stress conditions. The dominant physical mechanism of the low-temperature gate leakage current is identified to be Poole–Frenkel emission at low gate bias and Fowler–Nordheim tunneling at high bias. From the physical model, a more accurate lifetime projection can be obtained for given use conditions. [ABSTRACT FROM AUTHOR]