The epitaxial growth of oxides such as ZnO and ZnMgO by molecular beam epitaxy (MBE) is known to be difficult because the Si substrate surface is easily oxidized in the initial stage of growth. However, we have succeeded in solving this problem by depositing a thin Mg buffer layer on the (7 x 7) reconstructed Si(111) Surface prior to the growth of oxides. Good quality epitaxial ZnO layers are grown on such buffer layers. Successful growth of hexagonal ZnMgO films on Si(111) substrates is demonstrated by using Mg layer followed by MgO growth as a buffer layer. All the layers are grown by MBE using a radio frequency radical cell. The results of the glow discharge optical emission spectroscopy measurement indicate that Zn1-xMgxO films with Mg fraction x up to about 0.5 are obtained without phase separation. Moreover, these ZnMgO films are confirmed to be hexagonal c-oriented through the X-ray diffraction measurement and reflection high-energy electron diffraction observation. The lattice constant and cathodoluminescence peak energy are also investigated as a function of x. © 2005 Elsevier B.V. All rights reserved.