Excess charge carrier kinetics in p-doped crystalline silicon (Si) wafers covered by SiO2 films is investigated by transient photoconductance and surface photovoltage measurements. This makes it possible to distinguish between excess charge carriers collected in the Si/SiO2 heterojunction and those in the Si volume. The decay of the photoconductance signal in the millisecond time range could be unambiguously attributed to excess charge carriers stored in the space charge region. The decay of these charge carriers appears to be independent of the volume lifetime. The difference between the behaviours in Si/SiO2 and Si/SiNx is discussed.