A method is described for studying the backgating anomalies which are observed in GaAs FETS. It consists of device characteristics measurements of the substrate conduction at a temperature at which the transient is slow. The technique is verified by measurements on the properties of hole like traps using DLTS scan. The deep level impurity concentration is found to influence the backgating effect with the formation of the electric dipole layer at channel-substrate interface. The voltage drop in the semi-insulating substrate alters the device characteristics and limits the application of these devices in the field of wireless communication. The electric field at the junctions of drain, gate and substrate plays a critical role in the generation of low-frequency deep-level effects in GaAs FETS with or without backgating. The frequency of the deep level effects cause channel narrowing and shows high sensitivity to the ambient temperature.