The embedded Si structure formed by pattern-dependent oxidation (PADOX) in single-electron transistors (SET) is observed by two microscopic methods, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The top view of the Si nanostructure embedded in SiO2 is observed by a novel microscopic method, 'see-through' SEM. The side view of the embedded Si is revealed by a cross-sectional TEM observation with the focused ion beam (FIB) sample preparation. The potential profile defined by the observed shape of the embedded Si in the SET has only a single barrier due to the quantum confinement effect. This single barrier is split into two parts by the band gap reduction due to the strain effect of the oxidized Si. (C) 2003 Elsevier B.V. All rights reserved.