A semiconductor memory device and a method of operating the same are provided. The semiconductor memory device includes memory cells stacked on a substrate. The method includes applying a reference voltage to an unselected drain select line, applying a drain selection voltage to a selected drain select line, and applying a word line voltage to a normal word line. Before the word line voltage is applied to the normal word line, a positive voltage is applied to a dummy word line to bounce the unselected drain select line.