A nonvolatile semiconductor memory device comprising: a semiconductor substrate (20); and a memory transistor (100) including a source region (20S) and a drain region (20D) which are impurity diffusion layers formed in the semiconductor substrate, a tunnel insulating layer (25) formed on the semiconductor substrate, and a staked-structure gate electrode (20G) having a floating gate (24), a dielectric layer (23) and a control gate (22) which are layered on the tunnel insulating layer. The floating gate (24) is formed of a polysilicon layer having an impurity concentration of 1×1019 to 1×1020 cm−3. Denoting the impurity concentration of a polysilicon layer constituting the floating gate (24) as CFG and the impurity concentration of a polysilicon layer constituting the control gate (22) as CCG, it is preferable that the following relational expression (1) be satisfied: 0.3×CFG≦CCG≦0.8×CFG In the nonvolatile semiconductor memory device in the present invention, an impurity concentration of the polysilicon layer constituting the floating gate is in a specific range for preventing deterioration of the film quality of the tunnel insulating layer due to impurities contained in the floating gate, thereby making it possible to enhance characteristics such as an erase characteristic and a data retaining characteristic.