Design methodology and flow characterization of a miniaturized trickle-bed system for singlet-oxygen production via exothermic reaction of chlorine gas and basic hydrogen peroxide aqueous solution are reported. Miniaturized singlet oxygen production is accomplished by integration of several components developed for microsystems (uniform phase distributors, integrated on-chip cooling, and capillary-based phase separation) within a single device. Macroscale design equations for pressure-drop and heat-transfer rates are verified experimentally in the miniature trickle-bed reactor. Flow regime data from the present study are summarized with previous reports in microdevices and compared to conventional multiphase flow maps; these maps are found to be incapable of accurately predicting the flow regime trends within the miniaturized trickle-bed system. Operation of the silicon-based miniaturized trickle-bed reactor achieved estimated singlet-oxygen yields of 78%, comparing well with the reactor model predictions. © 2008 American Institute of Chemical Engineers AIChE J, 2008