In this paper a brief review of the polycrystalline silicon technology is first presented, with particular emphasis on the Low Pressure Chemical Vapour Deposition (LPCVD) technique, and the recrystallisation and grain boundary passivation approaches. This is followed by the presentation of the detailed studies on the phosphorus diffusion into LPCVD polysilicon and the grain boundary passivation effects on the thin film transistors carried out in our laboratory. © 1997 Taylor & Francis Group, LLC.