Zinc sulfide thin films have been produced from films of zinc oxide deposited by sol-gel techniques from a solution of metal alkoxide in ethanol. The oxide films were converted to zinc sulfide by annealing in a hydrogen sulfide-containing atmosphere. The conditions controlling the conversion of oxide to sulfide have been determined by observing the changes in structure and composition as a function of sulfidation temperature and annealing tithe. It has been found that, after an initial 'dead time', conversion takes place in a two-step manner where, for an initial period of approximately 60 min, little diffusion takes place followed by faster diffusion with a diffusion coefficient of 7.8 x 10(-18) m(2) s(-1), which is independent of sulfur concentration. It is also found that the sulfide forms the hexagonal phase with a strong (002) orientation.