Owing to the high bandgap of up to 4.8 eV, Ga₂O₃ has a natural advantage in the field of deep-ultraviolet (DUV) detection. The Ga₂O₃-based photoconductors, Schottky and heterojunction detectors are proposed and show excellent photodetection performance. The Ga₂O₃ heterojunction detectors are self-driven and feature low power consumption. On the other hand, considering the ultra-wide bandgap and low intrinsic carrier concentration, Ga₂O₃-based photodetectors are exhibiting important applications in high-temperature photodetection. In this work, a WO₃/β-Ga₂O₃ heterojunction DUV photodetector is constructed and the effect of high temperature on its detection performance is investigated. The β-Ga₂O₃ films are prepared by metal-organic chemical vapor deposition (MOCVD), and WO₃ films and Ti/Au ohmic electrodes are prepared by spin-coating technology and magnetron sputtering technique, respectively. The current-voltage (I-V) and current-time (I-t) measurements are performed at different ambient temperatures. Parameters including light-dark-current ratio (PDCR), responsivity (R), detectivity (D^*), and external quantum efficiency (EQE) are extracted to evaluate the deep-ultraviolet detection performance and its high-temperature stability. At room temperature (300 K), the PDCR, the R, the D^*, and the EQE of the detector are 3.05×10⁶, 2.7 mA/W, 1.51×10¹³ Jones, and 1.32%, respectively. As the temperature increases, the dark current of the device increases and the photocurrent decreases, resulting in the degradation of the photodetection performance. To explore the physical mechanism behind the degradation of the detection performance, the effect of temperature on the carrier generation-combination process is investigated. It is found that the Shockley-Read-Hall (SRH) generation-combination mechanism is enhanced with the increase of temperature. Recombination centers are introduced from the crystal defects and interfacial defects, which originate mainly from the SRH process. Specifically, the dark current comes mainly from the depletion region of WO₃/β-Ga₂O₃, and the carrier generation rate in the depletion region is enhanced with temperature increasing, which leads to the rise of dark current. Similarly, the increase of temperature leads to the improvement of the recombination process, therefore the photocurrent decreases at a higher temperature. This effect can also well explain the variation of response time at a high temperature. Overall, it is exhibited that the WO₃/β-Ga₂O₃ heterojunction photodetector can achieve stable self-powered operation even at an ambient temperature of 450 K, indicating that the all-oxide heterojunction detector has potential applications in harsh detection environments.