Abstract A simulation of dislocation sources in silicon is presented which has been developed in order to further examine how dislocation dynamics and multiplication govern the initial stage of plastic flow in diamond cubic crystals. The numerical method is adapted from an existing code by introducing specific dislocation properties deriving from the presence of strong Peierls forces. Most of the results obtained can be qualitatively interpreted in terms of the various contributions to the effective stress on the dislocation segments and of the particular character of the stress versus velocity laws in silicon. The backstresses in the slip plane and in the cross-slip plane are investigated in some detail in the conditions of the upper yield point. A first study of the yield point is also mentioned, which should permit to have a further examination of the well-known model by Alexander and Haasen.