This paper describes the FA technique to identify very tiny defects that cause gate oxide damage. These defects as examples include crystal originated pits, gate oxide pinhole and residual. The defects may have the same electrical signature; the same kind holes in gate oxide will be seen when the sample is simply deprocessed with wet chemical and observed with SEM; but they are distinctly different mechanisms. Electrical test, emission microscope, FIB and SEM were used to localize the defect and TEM for the final analysis. The application of planeview, cross-sectional and three-dimensional TEM is discussed.