The self-catalyzed growth of planar GaAs nanowires is analyzed using the lattice kinetic Monte Carlo model. Vapor–liquid–solid nanowire growth on (111)A and (111)B substrates is investigated. The effect of temperature and the location of gallium droplets on the morphology and growth direction of planar GaAs nanowires is examined. The temperature range of the stable growth of planar GaAs nanowires on the GaAs(111)A surface is revealed. Special asymmetric arrangement of the droplets is shown to ensure unidirectional nanowire growth.