By addition of Si to a binary transition metal nitride MN (e.g. TiN, ZrN, NbN, CrN), the hardness, thermal stability and chemical inertness of films have been considerably improved. The formation of a ternary M–Si–N ternary phase is possible under specific conditions such as low temperature, high deposition rate and low nitrogen pressure. The formation of nanocomposite materials (e.g. crystallites of MN + a thin layer of SiNx) is also possible under a wide range of deposition conditions. In such nanocomposite thin films the crystallite sizes are on the order of a few nanometers. The grain surfaces and boundaries have an important effect on the physical properties. The arrangement and chemical composition of the so-called “amorphous” minority phase (SiNx) are crucial for electrical and mechanical properties. The location, composition and thickness of the amorphous phase must therefore be known precisely. Their experimental determination is challenging due to the small concentration and in particular the geometry of the “amorphous” phase: approximately one monolayer either completely or partially covering the MN nanocrystallites. TEM investigations on such composites are known to have their limitations. It will be shown that the electrical resistivity, measured as a function of temperature, provides an experimental means for following the thickness evolution of the SiNx coverage layer, in such nanocomposite films.