Historically, it has been difficult to correlate the leakage current of capacitor structures involving high-k dielectric materials and defect states detected spectroscopically by the thermally stimulated current (TSC) technique. Four mechanisms are proposed and solutions are explained with tantalum oxide as an example. One of the mechanisms is the limitation of the TSC technique itself because of the presence of a parasitic current due to the bias voltage used. This can be solved by migrating to more advanced versions of TSC like zero-bias TSC or zero-temperature-gradient zero-bias TSC. In addition, another possible mechanism is that some defect states may have an electron repulsive energy barrier. Furthermore, another possible mechanism is that the leakage current may be insensitive to the presence of defect states under some situations; a unified Schottky-Poole-Frenkel model is proposed by the author to explain such a situation. Finally, another mechanism is due to the non-uniform distribution of defect states. Sometimes, this can be solved by using a 2-zone model proposed by the author. (C) 2012 The Electrochemical Society. [DOI: 10.1149/2.001206jes] All rights reserved.