Hydrogen annealing effects on silicon-on-insulator (SOI) materials are reported. High boron concentration of ∼2×1018/cm3 in 0.1-μm-thick SOI layer produced by bond and etch-back SOI (BESOI) method is reduced to ∼ 5×1015/cm3 by annealing at 1150 °C for 1 h. The BESOI surface became very smooth comparable to commercially available polished wafer simultaneously. Separation-by-implantation-of-oxygen wafer was also smoothed by the hydrogen anneal. This is due to surface migration of Si atoms driven by surface energy minimization after removing native oxide.