The determination of both the energy and the spatial distribution of interface states of an MOS transistor utilising charge-pumping measurements is described. The energy distribution of interface states is determined by measuring the charge-pumping current as a function of gate bias at several temperatures. Although the energy profile obtained shows several maxima and minima, a gradual increase in magnitude occurs as the band edge is approached. The spatial distribution of interface states is determined by measuring the frequency dependence of the charge-pumping current. The devices tested show an exponentially decreasing interface-state density away from the surface. Information is also obtained on capture crosssections from the frequency dependence of the charge-pumping current.