High resolution transmission electron microscopy has provided direct experimental evidence of monocrystalline, single-phase zinc-blende MgS. The authors report the first high resolution images of a metastable ß-MgS epilayer. This material naturally has rocksalt crystalline structure, but ß -MgS was grown in this work by molecular beam epitaxy on a ZnSe/MgS multilayer buffered GaAs (001) substrate using Mg and ZnS sources, following a simple procedure. A metastable ß-MgS layer of up to 125 nm thick has been examined using this technique. Embedded stacking faults are observed in the ß-MgS thick epilayer. © 2006 American Institute of Physics.