To determine the trap concentration of the deep levels in semiconductors, more exact formulation than used previously has been developed. As an example, we have selected molecular beam epitaxy-grown, Si-doped, low temperature (LT) GaAs and considered the lambda effect. The effect of reverse bias field and forward pulse on the deep level trap concentrations has been investigated. Experimental data were obtained from the field effect deep level transient spectroscopy measurement and capacitance voltage characteristics at appropriate temperatures. The LT-GaAs was found to possess rather high trap concentrations in all the deep levels included in the present investigation.