A method for manufacturing a semiconductor memory device including following steps is provided. A substrate having a first region, a second region, and a third region is provided. A first stack structure is formed on the first region. A second stack structure is formed on the second region. A third stack structure is formed on the third region. A first mask layer is formed on the substrate to cover the third stack structure. A first ion implantation process is performed, so that a second floating gate and a second control gate in the second stack structure are changed to a first conductive type. A second mask layer formed on the substrate to cover the first and second stack structures. A second ion implantation process is performed, so that a third floating gate and a third control gate in the third stack structure are changed as a second conductive type.