Accidental dielectric breakdown defects in thermally grown SiO2 films on p-type, Czochralski-grown, chemo-mechanically polished Si wafers with various optical precipitate profiling defect densities were investigated. The accidental oxide defect densities were estimated by time-zero and time-dependent dielectric breakdown measurements. In both dielectric breakdown measurements, the total accidental dielectric breakdown defect density in 10 nm thick oxide was almost the same as that of 25 nm thick oxide. The total accidental oxide dielectric breakdown defect density was almost consistent with the crystal originated particle (COP) density that appeared on the original wafer surface. This result indicates that only the COPs that are present on the wafer surface prior to gate oxidation are responsible for the accidental dielectric breakdown defects. The results in this report were obtained by a round robin of measurements from six wafer vendors and two researchers. (C) 2003 The Electrochemical Society.