SiO2/Si(111)interfaces formed by a furnace oxidation are studied by a scanning reflection electron microscopy (SREM). SREM observation indicates that the initial atomic steps on a Si(111) surface are preserved at theSiO2/Siinterface and the interfacial steps do not move laterally even after 48-nm-thick oxidation. A profile analysis of reflection high-energy electron diffraction shows that theSiO2/Siinterface consists of islands which have a diameter of about 5 nm and monolayer depth. Our results indicate that the layer-by-layer oxidation caused by two-dimensional island nucleation proceeds under furnace oxidation. ©1998 American Institute of Physics.