We study the growth of double-barrier insulator/Si/insulator nanostructures on Si(111) using molecular beam epitaxy. Based on different investigations, we develop an approach for the fabrication of nanostructures with continuous ultrathin single-crystalline silicon buried in a single-crystalline insulator matrix with sharp interfaces. The. approach is based on an epitaxial encapsulated solid-phase epitaxy, in which the solid-phase epitaxy of silicon is accompanied by a vapor-phase epitaxy of the second insulator layer. As an example, we demonstrate the growth of epitaxial silicon buried in epitaxial Gd2O3. The incorporation of epitaxial Si islands into single-crystalline Gd2O3 is also demonstrated. (c) 2006 American Vacuum Society.