Chemical bath deposition (CBD) is a commonly used and inexpensive technique to deposit a variety of semiconductor and oxide thin films for a variety of different applications. In this work, a continuous flow microreactor was used to better control the reacting flux present during the CBD reaction by offering a better temporal resolution. High quality CdS films at various thicknesses could be obtained by using a flux that avoided the formation of nanoparticles. The chemistry and growth kinetics of CdS CBD were elucidated using this microreactor. The results suggest that HS- ions formed during the thiourea hydrolysis reaction are the dominant sulfide ion source responsible for the CdS deposition.