Depletion region modulation (DRM) effect is often observed in photoconductance lifetimemeasurements of crystalline silicon wafers passivated by dielectric films. This effect is closelyrelated to the space-charge region electrostatically induced by fixed charges within the dielectric.This study proposes a model for dielectric-passivated c-Si wafers, which includes the DRM effect,to simulate and fit the effective lifetime vs excess minority carrier density curves obtained byquasisteady-state photoconductance techniques. The validity of the model is checked by applying itto different experimental samples, taking particular care of the mobility values of the surfacecarriers. It is, thus, demonstrated that the fixed charge within the dielectric film can be determinedwith improved accuracy and increased reliability if the DRM effect is included into the model.