FeS2 thin films were prepared by thermal sulfidation of iron layers evaporated on glass substrates. Experiments were carried out to optimize the sulfidation parameters. For this purpose, morphological, compositional, crystallographic, optical, and electrical properties of the produced films and their relation with the parameters involved in the sulfidation process (temperature, sulfur pressure) are presented. From x‐ray spectra and energy dispersive analyses of x ray it is concluded that FeS2 starts to be formed at sulfidation temperatures about 200 °C. X‐ray patterns show that crystallinity and grain size of the films improve with the sulfidation temperature with a ‘‘critical value’’ which varies with the sulfur pressure. On the other hand, both the film resistivity and the optical absorption coefficient change abruptly at temperatures higher than 350 °C. Above 500 °C polycrystalline aggregates known as ‘‘framboidal pyrite’’ are observed.