Ultrapure water is used in the final rinse stage of silicon wafer cleaning for ULSI fabrication. Recently, advanced ultrapure water production systems have been developed. They can supply ultrapure water in which any impurities are reduced to an extremely low level. Dissolved oxygen also has been reduced to ppb level for native oxide free processing. Further, Cr2O2 stainless steel piping has been also developed for continuous ozone injection sterilization in ultrapure water systems. In addition, it is becoming possible to develop perfectly controlled ultrapure water technolgies such as ozone-added-ultrapure-water rising for the removal of organic from wafer surfaces and boiling-ultrapure-water treatment for the realization of H-terminated wafer surfaces.