An expression for the free energy of nucleus formation from liquid phase of a catalyst during growth of III–V semiconductor nanowires (NWs) via the vapor–liquid–solid (VLS) mechanism has been derived with allowance for depletion of the number of atoms of the group V element (As) in the drop as a result of the island growth during As deposition from the gas–vapor phase. Various regimes of island formation, including a regime with growth arrest at small As concentrations in the drop have been theoretically studied. It is established that the growth arrest takes place when the As concentration decreases to an equilibrium level. The obtained results can be used in simulations of the growth kinetics of III–V semiconductor NWs, statistics of their nucleation, and NW length distribution functions, as well as for modeling of the crystalline phase growth and doping processes.