The effects of implantation temperature (Ti) on the chemical and physical structure of annealed high‐dose oxygen ion implanted layers were investigated by Auger electron spectroscopy (AES) and transmission electron microscopy (TEM). At lowTi(∼400 °C) the buried oxide is bordered by layers of polycrystalline silicon (polysilicon) which, in the top silicon layer, is separated from damaged single crystal Si by a thin band of discontinuous oxide. These polysilicon layers are formed from amorphous regions during high‐temperature anneals. At highTi(∼500 °C) polysilicon was not observed.