Both GaAs and Si single crystals were laser annealed with a 20‐ns ruby laser pulse. By means of a time‐of‐flight measurement the velocity distribution and the density variation of evaporated Ga or As and Si atoms were determined for different energy densities. Simultaneously the reflectivity of the crystal surface was measured time‐resolved. The data show consistently that the molten phase occurs at energy densities ≳0.35 J cm−2for GaAs and ≳0.8 J cm−2for Si. The results are in agreement with a purely thermal model for laser annealing.