Crystal phase control in single III–V semiconductor nanowires has emerged recently as animportant challenge and possible complement to conventional bandgap engineering insingle material systems. Here we investigate a supply interruption method for precisecrystal phase control in single nanowires. The nanowires are grown by metalorganic vaporphase epitaxy using gold particles as seeds and are analyzed by transmissionelectron microscopy. It is observed that wurtzite segments with controlled lengthand position can be inserted on demand into a pure InAs zincblende nanowire.The interface between wurtzite and zincblende segments can be made atomicallysharp and the segments can be made only a few bilayers in thickness. The growthmechanisms, applicability and limitations of the technique are presented and discussed.