A memory device of the invention has a P type substrate, a first drain area of N type formed in the substrate, a second drain area of N type formed in the substrate close to the first drain area, and a source area of N.sup.+ type formed around the first and second drain areas so that the source area continuously surrounds the drain areas from three sides, e.g., the right, left and top sides of these areas. The combination of the closed arrangement of the drain areas and the surrounding arrangement of the source area decreases minority carriers generated around the drain areas and prevents unbalanced carrier absorption of the drain areas, thereby suppressing the occurrence of a soft error.