We investigated the thermal stability and the electron irradiation damage of the ordered structure in the thermal oxide layer on Si substrates. The diffraction peak from the ordered SiO2 shifted to the lower angle side, and the intensity decreased after thermal annealing above 950 degrees C, indicating the decrease in density and the disordering of the structure. The least-squares fitting analysis assuming the quasi-amorphous structure showed that the ordered SiO2 was relatively stable at the SiO2/Si interface and the root-mean-square displacement of the atoms at the interface was 0.22 nm. The ordered structure was also degraded by electron irradiation at a dose of less than 6.6 C/cm(2). (C) 2010 The Electrochemical Society. [DOI: 10.1149/1.3476310] All rights reserved.