A reliable semiconductor memory device and an erasing method for erasing data in a reliable manner are provided. The erasing method is applied to erase a semiconductor memory device having a memory array, and the memory array has an NAND string. A predetermined voltage is applied to a gate of a select transistor of the NAND string, and the predetermined voltage is applied to a word line of a memory cell of the NAND string. An erasing voltage is applied to a substrate region at a first timing, and the substrate region has the NAND string. The gate of the select transistor is floated at a second timing. Here, there is a fixed time interval between the first timing and the second timing, and the second timing is later than the first timing.