The cathodoluminescence (CL) properties of m-plane α-Ga₂O₃ grown by mist chemical vapor deposition are investigated. The m-plane α-Ga₂O₃ is found to have two types of characteristic luminescence bands: blue luminescence (BL) band (centered at 2.8 eV) and UV luminescence (UVL) band (centered at 3.7 eV). To characterize these bands, the Sn concentration and temperature dependences of the CL spectra are investigated using samples with varying Sn concentrations from 1 × 10¹⁷ to 1 × 10¹⁹ cm⁻³. The Sn concentration-dependent CL spectra show that the luminescence from the UVL band is dominant in the low Sn concentration region, while that from the BL band is dominant in the high Sn concentration region. The temperature-dependent CL spectra indicate that the peak intensity of the UVL band depending on temperature is larger than that of the BL band. The activation energies in the UVL band of the undoped and lightly Sn-doped samples are determined as 110 meV. In addition, the parameters of the Huang–Rhys factor in the UVL band are obtained as 28.6 and 18.8, respectively. These results strongly suggest that the UVL band is derived from self-trapped excitons, which is the recombination of free electrons and self-trapped holes.