A post-breakdown resistance of SiO 2 has been studied as a quantitative monitor to describe the dielectric breakdown characteristics. First, a clear difference between dry and wet oxides is shown in terms of the post-breakdown resistance of SiO 2 as well as the charge-to-breakdown. Then, a boundary between hard- and soft-breakdown in sub-10nm SiO 2 is discussed from the viewpoint of a time constant for the energy dissipation in MOS closed circuit, through the statistical analysis of the post-breakdown resistance. The idea becomes more important in modeling and assessment of scaled-down CMOS device reliability.