Layered transition metal dichalcogenides (MoSe2, NbSe2) have been heteroepitaxially grown on (NH4)2Sx(x&bartil;2) treated GaAs(111)Ga, GaAs(∼(111))As surfaces in spite of the large difference in their crystal structures. Theinsituobservation of reflection high‐energy electron diffraction has shown that the grown film has its own lattice constant even from the first layer. The lattice matching condition, which is severely restricting in the usual heteroepitaxial growth case, is greatly relaxed in the present system because only weak van der Waals forces exist between the grown film and the substrate. This results from the fact that sulfur atoms regularly terminate dangling bonds on the GaAs surface after the (NH4)2Sxtreatment.