In this work an epitaxial Mg-Al spinel layer was successfully grown on a sapphire single crystal surface by solid-state reactions. An Mg film (15 mu m) was sputtered onto the sapphire crystal using RF magnetron sputtering. An epitaxial Mg-Al spinel layer was formed on the sapphire surface; an MgO layer was formed on top of the spinel layer by solid-state reactions that occurred around 1300-1600 degrees C, in an air atmosphere. When the reaction time was lengthened to over 30h at 1600 degrees C, these layers were almost completely transformed into an epitaxial Mg-Al spinel layer. The thickness of the epitaxial layer could be controlled by the length of the reaction time and the temperature. The results of X-ray diffraction analysis indicate that the orientation of the MgO and the spinel growth was dependent on the plane of the sapphire, that is (0001)(sapphire)parallel to(111)(spinel)parallel to(111)(MgO) and (1120)(sapphire)parallel to(111)(spinel)parallel to(111)(MgO). It was confirmed that the in-plane orientation of the spinel with respect to the C- and A-sapphire surface was [1100](sapphire)parallel to[110](spinel) , [1120](sapphire)parallel to[121](spinel) and [1010](sapphire)parallel to[110](spinel), [0001](sapphire)parallel to[112](spinel), and there would be (110)-oriented spinel growth on the M-plane sapphire substrate. (c) 2005 Elsevier B.V. All rights reserved.