Amorphous and microcrystalline silicon have been proven to be very interesting for low cost thin film photovoltaic devices. Usually these two materials are deposited using the same large area plasma-enhanced chemical vapor deposition reactors from silane and hydrogen gases. The transition from amorphous deposition regime to microcrystalline deposition regime is generally done by reducing the silane concentration in the input gas flow and the optimum deposition parameters to achieve high performance device stands just at the transition between the two microstructures. In the present work, a study of the transition width from amorphous to microcrystalline silicon is presented as a function of the input silane concentration. It is shown that the higher the input silane concentration, the wider is the microstructure transition. As a consequence, the process is less sensitive to fluctuations of the silane concentration when silane concentrations higher than 10 % are used and better uniformity and reproducibility can be then achieved.