The CO2laser annealing characteristics of high‐dose boron‐ and arsenic‐implanted silicon were studied by isothermal annealing experiments. A different annealing behavior at different annealing temperatures was found. At high annealing temperatures, a complete electrical activation was achieved, but after a prolonged annealing time, a relaxation of metastable concentrations takes place. At low doses, this phenomenon does not occur. The electrical activation energy is 5.8 eV for boron‐implanted silicon (1.3×1016cm−2, 120 keV), for annealing temperatures between 1045 and 1140 ° C.