Abstract Patterned arrays of gold-assisted vapor–liquid–solid (VLS) nanowires (NWs) were grown on Si(111) substrates by gas source molecular beam epitaxy (MBE). GaAs/GaP heterostructures were grown with periodic modulation of the group V composition. Study of these oscillations by high angle annular dark field (HAADF) scanning transmission electron microscopy (STEM) enabled the measurement of the instantaneous growth rate throughout the NW. Novel transient growth behavior, NW dissolution, droplet purging, and droplet refilling were observed to occur at the GaAs/GaP hetero-interface. These behaviors were linked to the large change in chemical potential difference between the liquid droplet and the crystal solid when switching between As and P.