Hexagonal MnAs thin films were grown on GaAs (100) substrates by using molecular beam epitaxy. The magnetization curve as a function of the magnetic field at 5 K showed that the MnAs thin films were ferromagnetic, and the magnetization curve as a function of the temperature revealed that the ferromagnetic transition temperature was as high as 318 K. The selected-area electron-diffraction pattern (SADP) and the high-resolution transmission electron microscopy (HRTEM) measurements on the MnAs/GaAs heterostructure showed that the hexagonal MnAs layer was grown pseudomorphically on the GaAs substrate. Based on the SADP and HRTEM results, a possible crystal structure for the MnAs/GaAs heterostructure is presented. (c) 2006 Elsevier B.V. All rights reserved.