We study the role of a Ti surface treatment applied to the As-terminated GaAs (001) substrate surface prior to SrTiO3 (STO) epitaxial growth by comparing STO/GaAs samples prepared with and without Ti interlayers. Reflection high energy electron diffraction, transmission electron microscopy and x-ray photoelectron spectroscopy are used to assess the structural and chemical properties of the layers and interfaces. Without Ti interlayer, a polycrystalline TiGa compound is formed near the interface. It significantly degrades STO structural properties. A Ti interlayer efficiently prevents the formation of this unwanted compound by limiting As desorption from the GaAs substrate during STO growth. It improves significantly the structural quality of the oxide layer. (C) 2015 Published by Elsevier B.V.