A semiconductor memory device and a manufacturing method of the same can effectively prevent deterioration of endurance characteristic which may occur in a data erasing operation, and a drain disturb phenomenon which may occur in a data writing operation. In the semiconductor memory device, an N-type impurity layer 3 is formed on a main surface of a P-type silicon substrate 1 located in a channel region. Thereby, a high electric field is not applied to a boundary region between the N-type impurity layer 3 and an N-type source diffusion region 10 during erasing of data, so that generation of interband tunneling in this region is effectively prevented. Also in this semiconductor memory device, the drain diffusion region 9 has an offset structure in which no portion thereof overlaps the floating gate electrode 5. Therefore, an electric field, which is generated across the floating gate electrode 5 and the drain diffusion region 9 in an unselected cell during writing of data, is weakened, as compared with the prior art, and the drain disturb phenomenon due to F-N tunneling is effectively prevented.