Atomic Insights of Irradiation-Induced Thermal Conductivity Degradation in β-Ga ₂ O ₃

β-Ga₂O₃ shows great potential for extreme-environment applications. However, its low thermal conductivity inevitably limits device reliability. Herein, the defect evolution and thermal conductivity degradation caused by irradiation along different β-Ga₂O₃ orientations are systematically investigated by simulations and experimental verifications. The simulation results suggest that Ga vacancies, O interstitials, and Ga_O antisite defects are the predominant defects after primary irradiation damage. Besides, a reordering of the anisotropic thermal conductivity after primary irradiation damage is observed, sequencing from κ_⊥(010) > κ_⊥(001) > κ_⊥(100) (before irradiation) to κ_⊥(010) > κ_⊥(100) > κ_⊥(001) (after irradiation). The experiments verify that the thermal conductivity of (100)-oriented β-Ga₂O₃ is significantly reduced by 34.38% after irradiation with a 2.0 MeV electron beam at a total fluence of 1.0 × 10¹⁷ cm^-2. This work clarifies the anisotropic degradation of thermal conductivity due to irradiation, providing atomic-level insights for optimizing the thermal transport properties in β-Ga₂O₃-based devices.