Conditions to remove contaminations adsorbed on a surface in wet cleaning processes have to be perfectly controlled. Megasonic excitation of ozonized water removes hydrocarbon contamination from silicon surfaces. When ozonized water was excited by megasonics at a frequency of about 1 MHz, OH radicals were produced in the cleaning solution. As a result, we have shown that hydrocarbons on the wafer surface were oxidized by OH radicals, leading to hydrocarbon-free Si surfaces.