Sn-doped beta-Ga2O3 single crystals with (100) plane were grown using the floating zone method, and the effect of the thermal annealing on the surface morphology, and electrical and optical properties was examined to compared with that before annealing. It was found that the surface morphology and roughness, electrical properties and optical transmittance did not change after annealing at 1100 degrees C in oxygen atmosphere, and the doped Sri was dispersed in beta-Ga2O3 matrix uniformly. However, the thermal annealing of Sn-doped beta-Ga2O3 causes the segregation of Sri atoms in the near-surface region, and the enhancement of the cathode luminescence (CL) intensity and the peak position toward longer wavelength. These results suggest that Sn-doped beta-Ga2O3 single crystal is thermally stable and is useful as substrate for the growth condition of GaN-based compounds. (C) 2007 Elsevier B.V. All rights reserved.