The characteristics of non-equilibrium charge in MOS capacitors on p-type 4H SiC with thermally grown nitrided gate oxides have been experimentally investigated for the first time. The reason for short relaxation time of capacitance recovery from deep-depletion to inversion levels has been identified: supply of minority carriers from the perimeter of the capacitors contributes to fast creation of the inversion layer. A negatively biased shielding ring has been employed to eliminate the lateral supply of minority electrons and to enable measurement of the effective generation rate.