Traditional GaN materials inevitably exhibit lattice mismatch and differing thermal expansion coefficients during epitaxial growth, which often leads to a sharp increase in dislocation density and interface defects. This results in severe current collapse, degraded high-frequency performance, and reliability degradation in GaN HEMT devices, representing one of the key bottlenecks facing GaN-based HEMT RF devices. Van der Waals epitaxial bonding between BN and GaN effectively suppresses dislocations and relieves material stress, playing a crucial role in enhancing the high-frequency performance and reliability of GaN HEMT devices. This paper fabricates AlGaN/GaN HEMT devices grown on BN buffer layers using van der Waals epitaxy. Test results indicate that compared to conventional devices without a BN buffer layer, not only has the on-resistance been reduced by 40% and the peak transconductance increased by 54%, but the maximum output current has also been boosted by 67%. Under strong negative gate voltage stress conditions, its performance significantly outperforms conventional devices, with a current collapse ratio of only 9.2%. During the pulse width reduction from 200 ms to 100 μs, only a minimal drift of approximately 0.09 V occurs. Under high-temperature conditions (125°C), the current collapse ratio is only 31%, with smaller reductions in transconductance and negative drift of Vth. The overall degradation is significantly lower than that of conventional AlGaN/GaN HEMT devices based on epitaxial systems, demonstrating excellent high-temperature dynamic stability. Additionally, RF performance improved, with fT increasing from 48 GHz to 90 GHz and fmax rising from 114 GHz to 133 GHz. This work fully demonstrates this interface optimization strategy simultaneously enhances carrier transport, suppresses trap effects, and improves RF performance, providing an effective pathway for realizing high-frequency, high-power, and highly reliable GaN HEMTs.