Anomalous impurity redistribution after a laser irradiation process in group-IV elements has been reported in numerous papers. In this Letter, we correlate this still unexplained behavior with the peculiar bonding character of the liquid state of group-IV semiconductors. Analyzing the B-Si system in a wide range of experimental conditions we demonstrate that this phenomenon derives from the non-Fickian diffusion transport of B in l− Si. The proposed diffusion model relies on the balance between two impurity states in different bonding configurations: one migrating at higher diffusivity than the other. This microscopic mechanism explains the anomalous B segregation, whereas accurate comparisons between experimental chemical profiles and simulation results validate the model.