In this article, the endurance characteristic of 3-D NAND Flash memory is investigated. The bitline (BL) current and the word-line (WL) current are measured for erase/write (EW) cycling up to 50k. Then, the trap profiles in the bandgap-engineered tunneling oxide (BE-TOX) layer are extracted through trap spectroscopy by charge injection and sensing (TSCIS) technique and technology computer-aided design (TCAD) simulation. The trap profiles show that the traps in the BE-TOX layer are generated toward the charge trap layer (CTL) side to the poly-Si channel side as EW cycling increases. Also, it shows that the deep traps below 2.0 eV start to be generated after 10k EW cycling and a double Gaussian distribution is fit well. Through the trap profile results, the degradation of both the BL current and the WL current according to EW cycling is completely explained.