Herein, the crystal phase switching between the cubic zinc-blende and hexagonal wurtzite phases in self-catalyzed GaAs nanowires (NWs) is theoretically studied, considering the dependence of the droplet contact angle on the position at the triple-phase line. This dependence is calculated for the droplets resting on the NW top facet, which has the shape of truncated hexagon. The nucleation of c and h islands, corresponding to the cubic and hexagonal crystal phases, at the triple phase line and in the center of the catalyst–NW interface, is considered within the classical nucleation theory. As a result, the probability of h-island nucleation as a
function of the average contact angle is obtained. It is found that the maximum of this probability shifts to the region of large contact angles when the length of narrow edges of the NW top facet decreases. Also, it is shown that the GaAs island nucleation at the triple-phase line occurs preferentially in the vicinity of the top facet corners.