Variation in stacking fault energy with annealing at 1173 K were identified in Czochralski-grown silicon crystals heavily doped with n - or p -type dopant atoms. In n -type crystals, the energy decreased with increasing annealing time. The higher the concentration of dopant atoms, the larger the degree of the decrease. On the other hand, the energy was unchanged during annealing in p -type and nondoped crystals. These results imply that n -type dopant atoms segregate nearby a stacking fault, via their thermal migration, under an electronic interaction leading to a reduction in the stacking fault energy.