The invention enhances program performance by increasing a coupling ratio between an N+ type source layer and a floating gate and reduces a memory cell area. Trenches are formed on the both sides of an N+ type source layer. The sidewalls of the trench includes first and second trench sidewalls that are parallel to end surfaces of two element isolation layers, a third trench sidewall that is perpendicular to the STIs, and a fourth trench sidewall that is not parallel to the third trench sidewall. The N+ type source layer is formed so as to extend from the bottom surface of the trench to the fourth trench sidewall, largely overlapping a floating gate, by performing ion-implantation of arsenic ion or the like in a parallel direction to the third trench sidewall and in a perpendicular direction or at an angle to a P type well layer from above the trench having this structure.