A structure of memory device includes trench isolation lines in a substrate, extending along a first direction. An active region in the substrate is between adjacent two of the trench isolation lines. A dielectric layer is disposed on the active region of the substrate. A floating gate corresponding to a memory cell is disposed on the dielectric layer between adjacent two of the trench isolation lines. The floating gate has a first protruding structure at a sidewall extending along the first direction. A first insulating layer crosses over the floating gate and the trench isolation lines. A control gate line is disposed on the first insulating layer over the floating gate, extending along a second direction intersecting with the first direction. The control gate line has a second protruding structure correspondingly stacked over the first protruding structure of the floating gate, and crosses over the trench isolation lines.