Abstract: In recent years, ultra-wide bandgap β-Ga₂O₃ has emerged as a fascinating semiconductor material due to its great potential in power and photoelectric devices. In semiconductor industrial, thermal treatment has been widely utilized as a convenient and effective approach for substrate property modulation and device fabrication. Thus, a thorough summary of β-Ga₂O₃ substrates and devices behaviors after high-temperature treatment should be significant. In this review, we present the recent advances in modulating properties of β-Ga₂O₃ substrates by thermal treatment, which include three major applications: (i) tuning surface electrical properties, (ii) modifying surface morphology, and (iii) oxidating films. Meanwhile, regulating electrical contacts and handling with radiation damage and ion implantation have also been discussed in device fabrication. In each category, universal annealing conditions were speculated to figure out the corresponding problems, and some unsolved questions were proposed clearly. This review could construct a systematic thermal treatment strategy for various purposes and applications of β-Ga₂O₃.