An apparatus for producing compound semiconductor thin films on substrates includes a reaction chamber wherein one or more constituents of semiconductor thin film is supplied as a gaseous species in a closed loop system. The apparatus includes hot and cold traps for isolating source materials from the reaction chamber and to provide for controlled delivery of the species. The hot and cold traps communicate with the reaction chamber through hot and cold legs to establish a closed loop recirculating flow. In a preferred embodiment, a thermosiphon provides the flow of gaseous species for formation of copper indium diselenide semiconductor thin films in a closed loop process.