SUMMARYEvidence from weak beam electron microscopy shows that dislocations introduced by deformation of crystals of tetrahedrally coordinated semi‐conductors are dissociated into partials, and suggests that these lie on the‘glide’ rather than the‘shuffle’ planes. Models of the structures of the cores of such partials are described, and it is proposed that the bonds in the cores of the 30° and 90° partials constituting screw and 60° dislocations are reconstructed, forming one dimensional super‐lattices, and that dangling bonds occur only at kinks, antiphase defects, and possibly in the cores of 60° partials constituting edge dislocations. The implications regarding electronic and optical properties are discussed briefly. Consideration of the charge carried by dislocations suggests that significant Coulomb forces between partials may arise only when Cottrell atmospheres of charged point defects or impurit