We report on the Au‐catalysed synthesis of GaAs nanowires on hetero‐structured GaAs/(111)Si substrates by metalorganic vapour phase epitaxy. It is demonstrated that the deposition of a 40‐50 nm thin GaAs epilayer onto Si guarantees a high percentage of straight and vertically‐aligned GaAs nanowires. GaAs epilayers were grown at 400 °C and subsequently annealed at 700 °C. Growth experiments performed on 4°‐miscut and exactly‐oriented (111)Si substrates show that a higher yield (close to 90%) of vertical nanowires is obtained using miscut substrates, an effect ascribed to the smoother surface morphology of GaAs epilayers on these substrates. Comparison between the cross‐sectional shape of nanowires grown on GaAs/(111)Si hetero‐substrates and those on (111)A‐GaAs and (111)B‐GaAs substrates demonstrates that both GaAs epilayers and over‐grown nanowires are (111)B‐oriented. (© 2011 …