Synchrotron radiation based photoemission has been used to investigate the thermal stability of HfO2 dielectric films deposited in-situ on ultra-thin thermally grown silicon oxide. Chemical interactions resulting in the limited formation of hafnium silicide is first detected at 700 °C. Progressively longer anneals at this temperature and subsequently at 800 °C results in the gradual reduction in thickness of the interfacial silicon oxide layer without a corresponding increase in the silicide signal. Annealing at 900 °C results in a complete removal of the interfacial oxide and a substantial increase in the silicide signal. These results suggest that the presence of a thin buffer oxide layer does not completely prevent silicide formation at 700 °C but plays an important role in increasing the decomposition temperature of the hafnium oxide layer to 900 °C. © 2011 Elsevier B.V. All rights reserved.