The authors describe a method for the determination of free carrier profiles in semiconductors which is particularly useful in the presence of high trap densities. The experimental procedure is based on high-frequency differential capacitance measurements of a Schottky or non-symmetrical pn junction which alternately undergoes forward bias and slow ramp reverse bias. The transient capacitance measurements just before emission occurs and after the traps emptying associated with the reverse biasing ramp (by the boxcar technique) give: the non-equilibrium C_NE-V characteristics in which the space charge is controlled by the free carriers only: the C_E-V characteristics at thermal equilibrium. The authors propose the acronym NECM (non-equilibrium capacitance method) for the technique. The method is tested with two commonly used treatments of silicon in device technology: gold-diffused and ion-implanted silicon.