The relationship between blocked or depleted lightly doped drain (LDD) implants and threshold voltage (Vt) shifts resulting in suppressed drive current has been thoroughly investigated and characterized through nano-probe analysis. In this paper, a review for a technique for characterizing Vt shift failures is presented as well as a brief review of the LDD Vt shift failure. A case study is also presented showing the characterization, identification, and the physical analysis results for the symmetrical Vt shift failure mechanism. The method presented allows the analyst to differentiate between a Vt shift failure caused by a depleted LDD implant mechanism and a failure caused by dopant depletion in the gate poly-silicon. The results demonstrate that there are now at least two failure mechanisms that can be responsible for threshold voltage failures and it is likely that there are more that have yet to be discovered.