Discharging process by multiple tunnelings is proposed and studied theoretically in thin-oxide MNOS structures. Traps at the silicon dioxide-silicon nitride interface and in silicon nitride layer are taken into account. Three tunneling processes are considered in the analysis. Those are (i) from the interface to silicon conduction band, (ii) from the silicon nitride layer to silicon conduction band, and (iii) from the silicon nitride layer to the interface (and then to silicon conduction band). From the analysis of these tunneling processes, physical interpretation for the maximum tunneling distance is derived.