We report on a silicon substrate preparation for Ill-V molecular-beam epitaxy (MBE). It combines sequences of ex situ and in situ treatments. The ex situ process is composed of cycles of HF dip and O-2 plasma treatments. Ellipsometry and atomic force microscopy performed after each step during the substrate preparation reveal surface cleaning and de-oxidation. The in situ treatment consists in flash annealing the substrate in the MBE chamber prior to epitaxial growth. GaSb-based multiple quantum well heterostructures emitting at 1.55 mu m were grown by MBE on Si substrates prepared by different methods. Structural characterizations using XRD and TOM coupled with photoluminescence spectroscopy demonstrates the efficiency of our preparation process. This study thus unravels a simple and reproducible protocol to prepare the Si surface prior to III-V MBE. (C) 2014 Elsevier B.V. All rights reserved.