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Both the static and kinetic properties of defects play fundamental roles in determining the physical properties of semiconductors. Compared to the static properties of defects, a comprehensive understanding of the different defects diffusing in different types of semiconductors is still lacking. In this article, based on extensive first-principles calculations, we have done a comparative study on the diffusion mechanisms of point defects in Si (a typical elemental semiconductor) and GaN (a typical compound semiconductor). The significantly different diffusion mechanisms of vacancies and interstitials in Si and GaN result in significantly different recombination mechanisms, i.e., a novel synergistic effect to accelerate the annihilation of defects is observed in Si but not in GaN, indicating that an efficient self-recovery mechanism can exist in Si but not in GaN. Our results not only explain some experimental observations in Si and GaN under nonequilibrium irradiation conditions but also provide a good example to understand the different kinetic properties of defects in elemental and compound semiconductors.