Ozonated water cleaning systems are used to remove photoresist and organic contaminants on silicon wafers and natural organic matter and bacteria in drinking water. In this paper, the effects of O 3 concentration, the system of ozonated water vapor, and substrate temperature on the removal efficiency of photoresist were investigated. A 11.59kcal/mol of activation energy was obtained for the reaction between aqueous O 3 and I-line photoresist. Increasing the process temperature increases the reaction rate of aqueous O 3 and photoresist, but reduces the solubility of O 3 in water for O 3 -injected system. Therefore, it is important to deliver aqueous O 3 to the wafer surface effectively. The removal rate of photoresist has been accelerated by controlling formation of a boundary layer as well as the temperature of the ozonated water and O 3 solubility. When water vapor was generated with O 3 and sprayed through a nozzle, the highest removal rate of photoresist, 221nm/min, was obtained. From the results observed in this study, it is concluded that it is important to have a fast uniform boundary layer formation, a thin boundary layer, and production of high concentrations of O 3 in the chamber in order to improve the removal efficiency of photoresist in the ozonated water system.