Using a Tersoff‐type empirical potential energy function, the free energy of formation for {113}‐type stacking faults in silicon has been calculated both as a function of stacking fault rod length and width at a variety of temperatures. A particular tetrahedral‐tetrahedral dimer has the lowest free energy of formation at 0 K and this type of stacking fault forms an assemblage of such dimers. The free energy of formation per interstitial in a ribbon fault decreases with ribbon width, ribbon length, and increase of temperature. ©1996 American Institute of Physics.