The results of Monte Carlo simulation of phase separation during binary film coevaporation are presented for a range of deposition conditions. The model employed assumes that phase separation occurs through surface interdiffusion during deposition, while the bulk of the film remains frozen. Simulations were performed on A‐B alloy films having compositions of 10 and 50 vol % solute. For both film compositions, the lateral scale of the domains at the film surface evolves to a steady‐state size during deposition. A power‐law dependence of the steady‐state domain size on the inverse deposition rate is obtained. Simulation microstructures at 50 vol % compare favorably with those obtained in a previous experimental study of phase separation during coevaporation of Al‐Ge films of the same composition. Results of simulations performed at 10 vol % are compared with the predictions of a theoretical model based on the above assumptions. The power‐law exponent obtained from simulations at 10 vol % is different than that predicted by the theoretical model. The reasons for this difference are discussed.