A semiconductor memory device includes a select transistor and a floating gate transistor on a substrate. The select transistor includes a select gate, a select gate oxide layer and a drain doping region. The floating gate transistor includes a floating gate, a floating gate oxide layer, a source doping region, a first tunnel doping region and a second tunnel doping region under the floating gate, a first tunnel oxide layer on the first tunnel doping region, and a second tunnel oxide layer on the second tunnel doping region. The floating gate oxide layer is disposed between the first tunnel oxide layer and the second tunnel oxide layer. A lightly doped diffusion region surrounds the source doping region and the second tunnel doping region.