The disclosure provides an erase method for a memory device. In the method, during a time period, a first positive voltage is applied to a body portion of a memory cell string of the memory device. The memory cell string includes memory cell transistors and select transistors connected in series. A second positive voltage is applied to a bit line signal of the memory cell string. A third positive voltage is applied to a first top select gate signal to turn on a first top select transistor of the select transistors so that the memory cell transistors are coupled to the bit line signal through the first top select transistor. A ground level voltage or a fourth positive voltage is applied to a word line signal of the memory cell transistors. Both the third and fourth positive voltages are less than the second positive voltage.