CdSe quantum dots (QDs) with narrow size distribution are synthesized continuously in a pressurized high-temperature microreactor using supercritical hexane as the main solvent. The as-prepared QDs exhibit narrow ohotoluminescence emission (full-width at half-maximum as small as 25 nm, corresponding to sigma = 4%), showing the advantages of supercritical-fluid synthesis compared to conventional high-boiling-point solvents.