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A new method is reported to measure the position and concentration of trap levels in semi-insulating materials where the regular deep level transient spectroscopy method is not applicable. In the proposed method, a transient space charge limited current (TSCLC) associated with the trap levels is measured using a capacitance balanced square wave voltage source, a voltage limiter-amplifier and a double box car averager. The TSCLC method is demonstrated on a p-type Y2.01Ca0.99Ge0.91Fe4.09O12 magnetic garnet sample ρ300=107 Ω cm. The trap level is located at 0.36 eV above the valence band edge and the concentration of the trapped holes is found to be 1013–1015 cm-3. [ABSTRACT FROM AUTHOR]