The dielectric breakdown is an irreversible and transient process, and it is difficult to understand its dynamic characteristics. We notice that the post-breakdown electrical properties of silicon dioxide films may include much information on the dielectric breakdown mechanism. First, the resistance of silicon dioxide films after the dielectric breakdown is statistically investigated, and then this analysis is applied to differentiate the hard- from the soft-breakdown. In particular, we discuss the critical dependence of the boundary between the hard- and softbreakdown on the discharging time constant as well as the discharging energy at the breakdown, concerning the formation of the conductive filament in the insulator silicon dioxide films. It should be noted that the ratio of the soft- to the hard-breakdown changes in terms of the statistical distribution in the case that the growth parameters and the measurement conditions are changed. In partcular, the external inductance effect to modify the discharging time constant in the MOS circuit is discussed. The thickness limitation of the silicon dioxide film in the roadmap is in this transition region, and this fact will be of essential importance in the assessment of the reliability and the process control of silicon device fabrication in sub-5nm silicon dioxide regime.