Since organic materials are easily damaged, failure analysis of electronic devices on flexible substrate using practice FA techniques is hard to procure. However, worse uniformity of organic thin film and high driving voltage may result in failures seldom discovered in conventional Si-based device. This paper aims to analyze the failures of organic thin-film transistors (OTFTs) by the techniques established in this study, involving non-destructive detection, and electrical failure localization. Results of this study showed that the existence of voids in the dielectric not only caused abnormality of electrical features, but also resulted in violent failure with high driving voltage punching. We successfully demonstrated the failure induced by high driving voltage, particular elongation of gate metal, using TEM observation. To conclude, analysis of electrical failure for flexible devices is the main object. This research is a great enhancement in failure analysis of devices and packages comprising organics and flexible substrate.