A new localization method called MF-TLS is introduced and applied in failure analysis praxis. The method combines local periodic thermal stimulation technique with periodic excitation of the electrical fails. The mixed frequency signal is detected by a lockin amplifier. MF-TLS was demonstrated on fabricated opens in a metal line and shown to be in semi-quantitative agreement with a capacitance modulation model. The technique was also applied to a scan shift problem and produced a higher sensitivity compared with other dynamic TLS methods. Limits and prospects of this new methodology are described.