We investigated core properties of dislocations in zinc-blende semiconductors using ah initio total energy calculations. The core reconstruction energy of partial dislocations was found to scale almost linearly with the experimental dislocation activation energy. The electronic band structure related to dislocation cores was also determined. In an unreconstructed core, the gap states comprise a half-filled one-dimensional hand, which splits up in bonding and antibonding states upon reconstruction. The energy states which lie in the electronic gap come from the cores of beta partials, while those related to alpha partials remain resonant in the valence band. (C) 2001 Elsevier Science B.V. All rights reserved.