We present a study on the morphological evolution of hydrogenated amorphous silicon layers obtained by plasma enhanced chemical vapor deposition at different H dilutions in the regime close to the formation of the nanocrystalline (nc‐Si) phase. The role of hydrogen in the transition from the amorphous to the crystalline phase is investigated by accurate structural and chemical characterisation, from the early stages of nucleation, where the nuclei present a size slightly larger than the critical nucleus, i.e. about 0.8 nm in radius, up to the formation of crystalline grains larger than 30 nm in radius. Hydrogen is found to have a crucial role in the transition from a‐Si:H to nc‐Si:H, since it forms an intermediate bond‐centred Si–H–Si configuration, and when the H moves away from the bond‐centred location, the strained Si–Si bonds either break or relax, undergoing local structural rearrangements closer to those of c‐Si …