A method is described for extracting the spatial distribution of charge stored in a charge-trapping layer of a semiconductor device. The method comprises the steps of performing a first charge-pumping measurement on a device under test using a variation of the upper level of the pulse and performing a second charge-pumping measurement on this device using a variation of the lower level of the pulse. The data obtained is combined for extracting the spatial distribution. This is done by establishing a relation between a charge pumping current I.sub.cp and a calculated channel length L.sub.calc of the semiconductor device by reconstructing spatial charge distribution estimates from the charge pumping curves for multiple values of the charge pumping current I.sub.cp. From these multiple values of I.sub.cp the value is obtained for which the corresponding calculated channel length L.sub.calc is substantially equal to the effective channel length L.sub.eff of the semiconductor device and the spatial charge distribution is reconstructed from the charge pumping curves using the obtained value of I.sub.cp.