AbstractX‐ray diffraction measurements on thin films of poly(hexyl‐pentylsilane) cast on silicon substrates are presented. The polymer chains pack in a hexagonal lattice which is oriented such that the chains lie parallel to the surface. In addition, a remarkable degree of orientational order was found with the planes containing the neighbor molecules lying in the surface plane. Parallel to the film surface, the average crystallite size is 600 Å, while perpendicular to the surface, there is nearly perfect interchain stacking of the polymers throughout the thickness of the