Mathematical modeling is presented to calculate the space charge limited current (SCLC) in a semiconductor containing traps at several discrete single energy levels. The effect of trap depths and trap densities is investigated in detail. If the difference in the trap energies is large, the J-V curves show humps as many as the number of trap levels. Each hump can be used to calculate a value of trap concentration. This trap concentration is the sum of all the traps at this and deeper energy levels. Accurate trap densities can only be obtained by fitting theoretical curve to the experimental J-V characteristics. The theory is compared with the experimental data taken from the literature. A very good agreement between theory and experiment is found. (C) 2009 Elsevier Ltd. All rights reserved.