A new variation of deep-level transient spectroscopy, suitable for depletion-mode field-effect transistors, is presented. It is similar to the conductance deep-level transient spectroscopy but does not require simultaneous measurement of the transconductance or the mobility for calculation of the trap concentrations. It is also independent of the transistor size and is very sensitive. The technique is demonstrated with measurements of radiation-induced traps in buried channel metal-oxide-semiconductor field-effect transistors which are used as output amplifiers in char ge-coupled device imagers. The unique structure of these transistors offers extended opportunities for studying the space distribution of the radiation-induced defects. In addition, we show a variation of the new transient technique using back-gate driving, which is applicable for studying the channel-substrate p-n junction, and the results are compared with those obtained from constant-capacitance voltage-transient measurements. Complementary measurements using front-gate and back-gate operation of the new technique can help to resolve the ambiguities usually associated with deep-level transient spectroscopy measurements of symmetrical p-n diodes.