We report a study of influence of charging and discharging in Si nanocrystals (nc-Si), which are embedded throughout the gate oxide in metal-oxide-semiconductor (MOS) structures, on the current-voltage and capacitance-voltage characteristics of the MOS structures. Very large current and capacitance are observed for the as-fabricated structures. However, charge trapping in the nanocrystals can reduce both the current and the capacitance dramatically. The trapped charges can also tunnel out from the nc-Si, leading to the recovery of both the current and the capacitance. The current reduction is attributed to the breaking of the nc-Si tunneling paths due to charge trapping in the nc-Si, while capacitance reduction is explained by an equivalent circuit in terms of the change of the nc-Si capacitance as a result of the charge trapping. (C) 2004 The Electrochemical Society.