For defects or impurities with deep energy levels, such as the commonly observed EL2, EL3, and EL6 in GaAs, it is very important to take account of the so‐called &lgr; effect in order to deduce the correct concentrations of these centers when using capacitance techniques. By measuring capacitance at several forward bias voltages for a given reverse bias voltage it is possible to determine concentrationNTand energyETwithout requiring the usual emission rate analysis. Convenient formulas forNTandETare given, although onlyNTcan be determined with a high degree of precision. The results for ann‐type horizontal Bridgman wafer (n&bartil;2.8×1016cm−3) are:NEL2=(1.14±0.02)×1016cm−3,EEL2(377 K)=0.71±0.06 eV;NEL6=(8.0±0.5)×1015cm−3,EEL6(167 K)=0.42±0.09 eV. ©1995 American Institute of Physics.