We report the self-catalysed growth of InAs1 − xSbx nanowires directly on bare Si substrates. Vertically aligned and non-tapered InAs1−xSbx nanowires were realized via indium-assisted nucleation without using nanowire stems. The compositions of the InAs1 − xSbx nanowires were determined by high resolution X-ray diffraction (HRXRD). It is observed that the geometry of the nanowires is modified by the Sb flux resulting in an almost doubling of the lateral dimension and a corresponding suppression in the axial growth of the InAs1 − xSbx nanowires. This observation unravels a method to modify the geometry of InAs nanowire and open up a promising route for the direct integration of InAs1 − xSbx nanowires with the well-established Si platform.