We have studied by XTEM the kinetics of Si amorphization by light ion implantation (He) as a function of substrate temperature. The analysis of these kinetics has been performed within the framework of the “Critical Damage Energy Density” model which is shown to apply for temperatures up to 250 K. There is a drastic change in the efficiency of the amorphization process at about 175 K. These results are discussed and explained by considering the different types of defects (I, V, I2, V2, complexes…) that can be stabilized in c-Si depending on the temperature. Above 150 K, the amorphization proceeds through the accumulation of interstitials and vacancies while at higher temperature it proceeds through the accumulation of di-interstitials and di-vacancies left in the network after annihilation and recombination of the Frenkel pairs created by the bombardment.