AbstractWe have grown zincblende‐structured ZnTeO alloy semiconductors on GaAs substrates by molecular beam epitaxy using RF‐excited O. O concentrations measured by secondary ion mass spectroscopy were found to increase with the increase of O2 flow rate supplied during the growth, while the change of lattice constant measured by X‐ray diffraction does not follow Vegard's law. It is considered that the O atoms are incorporated not only into group‐VI sites but also as interstitials. Formation of other compounds such as ZnTeO3, Zn2Te3O8, and TeO2 was not detected. Optical reflectance spectroscopy revealed the increase of the band‐gap energy with O concentration that can be interpreted as the repulsive interaction between the energy states originated in the localized states of O and the conduction‐band edge of host ZnTe. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)