A method to evaluate energy levels and densities of electron and hole traps in semiconductors from capacitance measurements on Schottky barriers and pn junction is presented. The occupation function for electrons at the deep level is derived, using Shockley-Read statistics for both forward and reverse biased junctions. The high frequency capacitance change before and after forward bias is applied is derived as a function of reverse voltage both for hole and electron traps. The experimental procedure to determine energy levels and the density of the traps is presented along with experimental results on silicon and gallium arsenide Schottky barriers and p+n junctions demonstrating the validity and limitations of the method.