We have investigated the thickness increase of buried oxide layers in silicon-on-insulator structures by thermal oxidation of the top silicon layer. A thermodynamic model is derived based on the experimental observation that oxidation introduces an oxygen concentration into silicon which is above its solubility limit. Experiments on buried oxide growth by thermal oxidation of the top silicon layer were performed with specially designed bond-and-etchback silicon-on-insulator structures in the temperature range between 1100 and 1200 degrees C. The results obtained are compared to the thermodynamic model and to data from other growth experiments. The different buried oxide growth rates observed for different types of silicon-on-insulator material are discussed in terms of different silicon self-interstitial supersaturations which are induced in the top silicon layer during oxidation.