The research of ultraviolet photodetectors (UV PDs) have been attracting extensive attention, due to their important applications in many areas. In this study, PtSe₂/GaN heterojunction is in-situ fabricated by synthesis of large-area vertically standing two-dimensional (2D) PtSe₂ film on n-GaN substrate. The PtSe₂/GaN heterojunction device demonstrates excellent photoresponse properties under illumination by deep UV light of 265 nm at zero bias voltage. Further analysis reveals that a high responsivity of 193 mAdW^-1, an ultrahigh specific detectivity of 3.8 × 10¹⁴ Jones, linear dynamic range of 155 dB and current on/off ratio of ~ 10⁸, as well as fast response speeds of 45/102 njs were obtained at zero bias voltage. Moreover, this device response quickly to the pulse laser of 266 nm with a rise time of 172 ns. Such high-performance PtSe₂/GaN heterojunction UV PD demonstrated in this work is far superior to previously reported results, suggesting that it has great potential for deep UV detection.