LaAlO3 films sputter-deposited on Si were submitted to rapid thermal annealing at 800 and 1000 degrees C. Atomic transport and chemical changes were investigated using ion beam analysis and X-ray photoelectron spectroscopy. Annealing induced La and Al losses or their migration into a newly formed interfacial layer and Si migration into the film. The mechanism of Si incorporation into the film is influenced by the annealing atmosphere. These instabilities were hampered by a thermal nitridation in NH3 at 700 degrees C performed prior to rapid thermal annealing, indicating a possible route for producing a thermally stable La-based high-kappa gate dielectric.