<p>The practical application of Ga₂O₃ photodetectors is constrained by low responsivity, long decay time, and external power reliance, whereas Nb₂CT_x MXene demonstrates a high work function and intrinsic solar-blind UV selectivity. Integrating Nb₂CT_x with Ga₂O₃ to form a suitable heterostructure offers a promising solution for significantly enhanced photodetection performance. Herein, a new type of self-powered photoelectrochemical (PEC) solar-blind UV photodetector has been constructed based on the heterostructure composed of β-Ga₂O₃ nanoarray rods and few-layered Nb₂CT_x via hydrothermal growth, post-annealing, spin-coating, and thermal processing. The photoelectric properties of the devices have been evaluated systematically. The results show that the β-Ga₂O₃/Nb₂CT_x heterojunction photodetector exhibits stable self-powering ability and typical solar-blind UV response characteristics. Under 254&#xa0;nm UV light illumination at 0&#xa0;V bias, the device achieves a photo-to-dark current ratio of 36.6 ± 4.85, responsivity of 2.4 ± 0.18&#xa0;mA/W, and specific defectivity of (3.12 ± 0.16) × 10¹⁰ Jones, showing 3.2, 2.3, and 4.1 times higher than those of pristine β-Ga₂O₃ device. Moreover, the β-Ga₂O₃/Nb₂CT_x heterojunction photodetector has a faster response speed, with a rise/decay time of 2.1&#xa0;s/0.6&#xa0;s. The improved photoresponse properties of the device are attributed to the built-in electric field established by the β-Ga₂O₃/Nb₂CT_x heterojunction, which can facilitate the transportation of photogenerated carriers and suppress electron–hole recombination. The present work not only extends the application of Nb₂CT_x&#xa0;MXene, but also provides a new tactic to improve the performance of Ga₂O₃-based photodetector.</p>