As semiconductor technology keeps scaling down, the conventional physical failure analysis processes have faced increasing challenges and encountered low success rate. It is not only because the defect causing a failure becomes tinier and tinier, but also because some of these defects themselves are invisible. Electrical nano-probing with narrowing down a defect to a single transistor has greatly increased the likeliness of finding a tiny defect in subsequent TEM (transmission Electron Microscope) analysis. However, there is still an increasing trend of encountering an invisible defect at most advanced technology nodes. This paper will present how to identify the root causes of three such invisible defects with the combination of electrical nano-probing and TEM chemical analysis.