High‐temperature oxygen ion implantation has been used to form buried oxide layers in silicon single crystals. The ion implantation and substrate variables, particularly the substrate temperature, were optimized to obtain silicon layers with controlled microstructures near the surface. The as‐implanted specimens were subsequently annealed at high temperatures to form a buried SiO2layer with sharp interfaces and to minimize dislocation densities in the top silicon layers. The specimens were characterized by cross‐section transmission electron microscopy and these results were compared with those obtained using spectroscopic ellipsometry. We discuss the application of the nondestructive scanning ellipsometry technique in the characterization of silicon‐on‐insulator materials.