We report in-situ measurements of impedance spectroscopy during flash experiments with single crystals of cubic-yttria stabilized zirconia, conducted in ambient air at 300 °C to 700 °C under a direct current electric field. Platinum electrodes transition from blocking to non-blocking behavior just before the onset of flash, indicating a transition to partial electronic conductivity during the incubation period. Even though the conductivity continued to increase with temperature the electron transport remained at a plateau of 0.25. This result has ramifications not only in the fundamental understanding but also in technological significance of the flash phenomenon.