Proton implantation and thermal annealing of silicon result in the formation of a specific type of extended defects involving hydrogen, named “platelets” or “cavities.” These defects have been related to the exfoliation mechanism on which a newly developed process to transfer thin films of silicon onto various substrates is based. The density and the size of these platelets depend on the implantation and annealing conditions. In this letter, rigorous statistical methods based on transmission electron microscopy have been used to quantitatively study the thermal behavior of these defects. Upon annealing, it is shown that the cavities grow in size, reduce their density, while the overall volume they occupy remains constant. This phenomenon is due to a conservative ripening of the cavities. The transfer of hydrogen atoms from small to large cavities leads to a decrease of the elastic energy within the implanted layer while the strain locally increases around the projected range of the protons. © 2000 American Institute of Physics.