The surface morphology of zinc blende MgS layers grown on ZnSe buffer layers has been investigated by atomic force microscopy (AFM). Under certain growth conditions, 1D nanowires form on the surface and both their dimensions and distribution are sensitive to the growth parameters used. We have investigated the nanowire formation as a function of flux ratio and MgS layer thickness. In thin MgS layers, the nanowires form bunches with atomically flat regions between them. In thicker MgS layers, the wires increase in size and density with the elimination of the flat regions between bunches of wires. This method of wire formation is consistent with an anisotropic relaxation of the MgS layer by mismatch dislocations leading to a surface instability by the Asaro-Tiller Grinfield mechanism. (c) 2006 Elsevier B.V. All rights reserved.