Abstract—: A precise model for calculating the dependence of the composition of self-catalyzed Ga(As,P) nanowires on the growth parameters without any fitting parameters is proposed. It is shown that the Ga(As, P)-nanowire composition does not depend on the growth rate at a fixed ratio of the total fluxes of Group-V- and Group-III atoms. The results of modeling are in good agreement with the experimentally observed dependence of the Ga(As,P) nanowire composition on the ratio of the fluxes of As and P atoms.