Retention of non-equilibrium charge in MOS capacitors on p-type 4H SiC with thermally grown nitrided gate oxides have been experimentally investigated. The reasons of short charge-retention time in this type of capacitors compared to n-type MOS capacitors have 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 carriers (electrons) and to enable measurement of the effective generation rate. (C) 2004 Elsevier B.V. All rights reserved.