We report a new and surprising enhancement of the electric field at the Si/SiO2 interface following the cessation of intense pulsed near-infrared radiation. The phenomenon, measured by optical second-harmonic generation, occurs only for photon energies and oxide film thickness that exceed respective thresholds. We attribute the new effect to multiphoton hole injection into the oxide and to an asymmetry in electron and hole dynamics, in particular to distinctly different trapping and detrapping processes.