A memory includes a first portion, a second portion and a controller. The first portion includes a first word line to a kth word line. The second portion is formed above the first portion and includes a (k+1)th word line to an mth word line. When an xth word line is used to perform a program operation, the controller is used to apply a first voltage to the first word line to an (x−2)th word line, a second voltage to an (x−1)th word line, and a third voltage to an (x+1)th word line. x, k and m are positive integers.