A semiconductor device includes: a memory cell transistor which has a floating gate, a control gate, and a source and a drain formed in a semiconductor substrate on both sides of the floating gate via a channel area; and a selecting transistor which has a select gate and a source and a drain formed in the semiconductor substrate on both sides of the select gate, wherein the source of the selecting transistor is connected to the drain of the memory cell transistor, the source of the memory cell transistor has an N-type first impurity diffusion layer, an N-type second impurity diffusion layer deeper than the first impurity diffusion layer, and an N-type third impurity diffusion layer which is shallower than the second impurity diffusion layer, and an impurity density of the second impurity diffusion layer is lower than that of the third impurity diffusion layer.