In this letter, we separated the corner and plane component of trap-assisted tunneling (TAT) mechanism and analyzed the retention characteristics in the world’s smallest NAND flash memory (1X-nm generation). We found that the Ea of the corner component in TAT mechanism is smaller than that of the plane component due to the higher crowding electric field and larger trap density. The extracted Ea of both the components at the highest programmed V th level (i.e., PV3 state) is smaller than that at PV2 state since the larger number of the stored electrons in floating gate increases the electric field across the tunneling oxide layer. It reduces the energy barrier between the traps and Ea . The ratio of the corner part over the plane one is larger at highly cycled and in smaller devices. For better understanding of the abnormal retention characteristics, each failure mechanism should be accurately analyzed.