Most recently low-dose (4E17 ions/cm(2)) SIMOX technology has been developed in order to restrain the dislocation density and the production cost. However, in- and out-diffusion of oxygen and internal oxidation (ITOX) phenomena have never been understood during high-temperature annealing process as yet. In this study, we use the sample, which was implanted O-18(+) with the dose of 4E17 ions/cm(2) into silicon substrate and then non-oxidizing anneal was done at around 1300 degreesC. As the results, it was proven that the diffusion of oxygen into thermal oxide layer above 1300 degreesC was not in agreement with the Deal-Grove theory. The mechanism of oxygen in- and out-diffusion in SIMOX wafer is discussed. (C) 2002 Elsevier Science B.V. All rights reserved.