A memory device includes a memory string and a control circuit coupled to the memory string. The memory string includes a top select gate, word lines, and a bottom select gate. The control circuit is configured to, in an erasing operation, apply an erasing voltage to the memory string, apply a verifying voltage to at least one word line of the word lines after applying the erasing voltage to the memory string, and apply a first turn-on voltage to the bottom select gate, before applying the verifying voltage to the at least one word line.