We used a side view transmission electron microscopy (TEM) technique which allows us to study the oxidation process of Si dots onSiO2systematically for different dot sizes, oxidation times, and temperatures. Using energy filtering TEM (EFTEM) an excellent contrast between Si andSiO2is achieved, independent from the crystal orientation. Si dots onSiO2with initial diameters from 10 to 60 nm were oxidized with different oxidation times at 850 °C. The resulting shapes of theSiO2and the embedded Si cores were determined from the EFTEM micrographs. A strong retardation of the oxidation process compared to planar oxidation as well as a self-limiting effect for long oxidation times are reported. Furthermore a pattern dependent oxidation is observed, depending on the aspect ratios of the dots.