A criterion for the growth of Stranski–Krastanov islands mediated by surfactants is obtained. It involves that surfactants decrease the island nucleation barrier. Thereby, at a low coverage (θ ≪ 1 mono layer) surfactants facilitate islands formation. At a high coverage (θ ≈ 1 mono layer) the islands growth might be still facilitated, but also hampered under special conditions. The latter is caused by the reduction of the ad-atom surface diffusion. We report on a non-monotonic dependence of Ge/Si(100) island array density on the Sb coverage and discuss it in the frame of the obtained criterion.