Amorphous InGaZnO 4-x S x thin films were fabricated using a polycrystalline InGaZnO 4 target by pulsed laser deposition in an H 2 S gas flow. The optical band gap first decreased from 3.05 to 1.65 eV as x increased from 0 to 1.5, and then increased to 2.6 eV at larger x, showing a bandgap bowing behavior. All the sulfur-containing films have high resistance beyond our measurement limit. Film density of the a-InGaZnS 4 film was decreased by ³40% from that of a-InGaZnO 4. Density functional theory calculations were performed to explain these results.