GaAs nanowires and GaAs/Fe3Si core/shell nanowire structures were grown by molecular-beam epitaxy on oxidized Si(111) substrates and characterized by transmission electron microscopy. The surfaces of the original GaAs NWs are completely covered by magnetic Fe3Si exhibiting an enhanced surface roughness compared to the bare GaAs NWs, due to formation of nanofacets. Growth of the shells at the substrate temperature of T-S = 200 degrees C leads to a regular nanofacetted growth of the Fe3Si shell. The resulting facets of the shells were analyzed, which lead to thickness inhomogeneities of the shells. They consist mainly of well-pronounced Fe3Si(111) planes. The crystallographic orientations of core and shell coincide. The nanofacetted Fe3Si shells found in the present work are probably the result of the Vollmer-Weber growth mode of Fe3Si on the {110} side facets of the GaAs NWs. (C) 2015 Elsevier B.V. All rights reserved.