This work presents an application of microfabricated reactors and detectors for photochemical reactions. Two fabrication schemes were demonstrated for the integration of the reaction and the detection modules: coupling individually packaged chips, and monolithic integration of the two functions. In the latter fabrication scheme, we have succeeded in bonding quartz wafers to patterned silicon wafers at low temperature using a Teflon-like polymer—CYTOP™. Using quartz substrates allows reaction and detection with UV light of lower wavelengths than Pyrex substrates permit. The pinacol formation reaction of benzophenone in isopropanol was the model reaction to demonstrate the performance of the microreactors. The extent of reaction was controlled by varying the flow rate and therefore the on-chip residence time. Crystallization of the product inside the microreactors was avoided by the continuous-flow design. Instead, crystallization was observed in the effluent storage device. Off-chip analysis using HPLC confirms the results obtained from the on-line UV spectroscopy. The quantum yield estimated suggests that the reactor design is effective in improving the overall efficiency of the reactor unit.