Metal chalcogenides – because of their excellent optical and electrical properties – are important semiconductor materials for optical devices, such as solar cells, sensors, and photocatalysts. The challenges associated with metal chalcogenides are the complexity of the conventional synthesis methods and the stringent synthesis conditions. In this study, the synthesis conditions were simplified in a solvent‐free synthesis method using cadmium precursor, thiourea and selenium to synthesize metal chalcogenides, such as CdS and CdSe, which have particularly suitable band gaps for the optical devices. CdSxSe1‐x solid solution was successfully synthesized under molten thiourea as the reactive reaction medium at relatively low temperatures, even at 180 °C, with residual melamine derivatives in the solid phase. The luminescence properties of CdSxSe1‐x and the products in the gas and solid phases were investigated. Optimization of the synthesis conditions for solid solutions of CdSxSe1‐x and the role of organic compounds in the formation of metal chalcogenides are discussed.