The transformation of dislocation cores from the shuffle to the glide set of {111} glide planes in Si is examined in this work. The transformation is thermally activated and is favored by a resolved shear stress which applies no force on the original perfect shuffle dislocation. A resolved shear stress driving dislocation motion in the glide plane is not observed to promote the transition. The stress-dependent activation energy for the described shuffle-glide transformation mechanism is evaluated using a statistical analysis. It is observed that the transformation is not associated with an intermediate metastable state, as has been previously suggested in the literature.