We present detailed results about the molecular beam epitaxy (MBE) growth of GaAs nanowires (NWs) on GaAs (111)B substrates prepared for the growth by a new method using hydrogen silsesquioxane (HSQ). Before the growth, HSQ is converted to SiOx by thermal treatment. The NWs are grown via the vapor-liquid-solid (VLS) mechanism. The influence of five growth parameters are described: SiOx thickness, growth time, substrate temperature and Ga and As-4 beam fluxes. It is shown that the nanowire density can be tuned by two orders of magnitude by adjusting the SiOx thickness. Additionally, the results demonstrate that the axial growth is controlled by the As-4 beam flux whereas the lateral growth is controlled by the Ga beam flux. The observed NW tapering is mainly determined by the Will beam flux ratio. Our study gives important information about the VLS growth mechanism, which is extended by considering the secondary adsorption process of Ga adatoms. The nanowires have predominantly zinc blende crystal structure with rotational twins. A wurtzite segment is always found at the top of the NWs being associated with the growth after the Ga shutter has been closed. (C) 2012 Elsevier B.V. All rights reserved.