A continuous reaction system (CRS) allows a method to prepare quantum dots (QDs) in a continuous manner with high precision. The CRS pumps a plurality of reagent fluids into one or more mixing sites to form a reaction fluid that is carried through a heating chamber at elevated pressures to carry out hydrothermal growth of the QDs. The pumps and heating chamber are controlled with a high precision by employing a detector downstream of the heating chamber to provide a signal that is dependent on the composition and size of the QDs. The signal is provided to a signal processor that provides a signal that control the flow rates and temperature parameters in the system. The QDs produced in this manner are consistent in size and composition and can be of a single semiconductor composition or can be core-shell QDs with a shell semiconductor formed on a core semiconductor.