A method for manufacturing a semiconductor device according to the present invention, comprising the steps of: forming a screen oxide layer over the surface of an active region of a semiconductor substrate in which an isolation structure defining the active region is formed; forming a first recess pattern in the active region and a second recess pattern in the isolation structure by etching a gate forming area in the active region and the isolation structure part extended thereto; removing the screen oxide film and simultaneously expanding the width of the second recess pattern; forming a first insulation dielectric layer over the resultant of the substrate having the second recess pattern with the expanded width so that the first insulation dielectric layer is blocked at the upper end thereof in the first recess pattern and it is deposited along the profile in the second recess pattern; forming a second insulation dielectric layer over the first insulation dielectric layer so that the second recess patter is not filled; forming a third insulation dielectric layer over the second insulation dielectric layer so that the second recess pattern is filled; and removing the third, second, and first insulation dielectric layers formed over the active region including the first recess pattern and the isolation structure between the second recess patterns.