A memory device includes a substrate, first and second trench isolations, a plurality of line-type isolations, a first word line, and a second word line. The substrate comprises an active area having source and drain regions. The first and second trench isolations extend parallel to each other. The line-type isolations define the active area together with the first and second trench isolations. The first word line extends across the active area and is formed in the substrate adjacent to the first trench isolation defining a first segment of the active area with the first trench isolation. The second word line extends across the active area and is formed in the substrate adjacent to the second trench isolation defining a second segment of the active area with the second trench isolation. The size of the first segment is substantially equal to the size of the second segment.