The control and determination of Zn1-x-yMgxBeySe quaternary alloy composition grown by molecular beam epitaxy was investigated. Compositions x and y of Zn1-x-yMgxBeySe were measured by inductive coupled plasma atomic emission spectrometry (ICP-AES). The energy band gap of Zn1-x-yMgxBeySe can be controlled in a range of 2.9 eV < E-g < 3.0 eV under nearly lattice matching condition to GaAs substrate. (C) 2003 Elsevier B.V. All rights reserved.