Abstract. Hydrogen implantation in silicon and subsequent thermal anneal result in the formation of a wide range of point and extended defects. In particular, characteristic two-dimensional extended defects, i.e. platelets, are formed. The growth of these defects during thermal anneal, related to H migration, induces the development of micro-cracks in Si. In this paper, a time dependence study of H defects during isothermal anneals is performed using SIMS, FTIR and TEM techniques. We calculate the kinetics of H 2 formation based on SIMS depth profiling and FTIR measurements. We show that the splitting is determined by H migration and rearrangement of hydrogenated defects.