We overview plasma-enhanced chemical vaper deposition (PECVD) of high-quality thin-film silicon. In PECVD, such a film is grown by the deposition of precursors, which is generated by the gas-phase reactions of source gases in plasma. The growth of the film depends on the surface reactions of precursors and the reactions in the growing film, i.e., in-film reactions, which influences the film structure and properties. The in-film reactions also take place after the growth, i.e., post-growth annealing. So, the reactions should be properly controlled throughout the growth and annealing for the high-quality film formation. Here, the growth kinetics and related reactions are presented for device-grade hydrogenated amorphous silicon (a-Si:H) films.