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We report on a method to deposit iron pyrite thin films via chemical bath deposition of Fe-O-S thin films followed by their thermal treatment in a sulfur-rich ambient. The deposition is made on glass substrates from an aqueous solution mixture of iron(III) nitrate, sodium thiosulfate, triethanolamine, and HCl added to adjust the pH between 7-8. After 2.5 h of deposition at 40 • C, a uniform specularly reflective amorphous film with thickness of 315 nm is obtained with a S:Fe ratio of 0.44 and significant oxygen content. Optical bandgap (E g ) of this material is 2.56 eV. Upon heating this film in a N 2 /S ambient at 400 • C for 3-10 h, a dark-gray mirror-like film is obtained. The film attains a granular morphology and the S:Fe ratio approximates to 2. This thin film is polycrystalline with cubic structure, as that of FeS 2 -pyrite phase, with crystallite diameter of 15 nm. Orthorhombic FeS 2 -marcasite is present as a minor phase in the film. The film possesses optical absorption coefficient 2 × 10 5 cm −1 in the visible region; indirect E g of 0.85 eV; p-type electrical conductivity of 1.2-2.1 −1 cm −1 showing photoconductivity; carrier density, 3 × 10 17 cm −3 ; and Hall mobility, 14 cm 2 V −1 s −1 .