Rutherford backscattering measurements have revealed that the buried amorphous layer formed in the silicon‐on‐sapphire (SOS) film by oxygen implantation with a dose of 1×1015/cm2at 130 K reorders epitaxially from the surface, and crystalline quality is improved in the entire region of the SOS film after annealing at 1000 °C for 20 min in N2. But in the case of implantation with a dose of 1×1016/cm2at room temperature, the high concentration of oxygen prevents the reordering and as a result the crystalline quality improvement is limited only in the surface region. Energy dependence of the dechanneled fraction shows that the type of defects in Si near the Si/sapphire interface has changed probably from microtwins or stacking faults to dislocation loops after reordering.