It has been newly found that shorter intervals between program and erase operations can suppress the oxide degradation more significantly in a 0.05 to 5 sec timeframe. Our new analysis clearly demonstrates the following degradation phenomena: a longer interval yields more trapped charges near the Si surface and surface states. Our results also indicate that the oxide degradation occurs more significantly during the erase-to-program interval than in the program-to-erase interval. These findings suggest that the erasing step causes a self-induced positive FG potential yields an accumulation of trapped holes near the Si surface and also generates surface states during the interval from erase-to-program. In addition, regarding retention characteristics, larger Vt shifts caused by the reduction of surface states and electron detrapping of oxide charges are observed in the longer interval. Based on these results, a new NAND operation scheme is proposed to improve reliability in shorter intervals.