The transient charge trapping and detrapping of a thick SiO2/Al2O3 gate oxide device has been evaluated by single pulse I-d-V-g (PIV). During the period of a single pulse, we observed fast electron detrapping. This occurred through the gate electrode, causing a counterclockwise PIV hysteresis despite electron injections from the channel region. The hysteresis direction transitioned from counterclockwise to clockwise as a function of pulse base level and peak level. The trap energy level of Al2O3, extracted by PIV at various temperatures, was found to be in the range of 1.14-1.39 eV, indicating the Frenkel-Poole defect band.