A method of fabricating a flash memory device includes sequentially forming an etching object layer and a lower sacrificial layer on a substrate, and forming an upper sacrificial pattern structure on the lower sacrificial layer. The upper sacrificial pattern structure includes an upper sacrificial pad portion and an upper sacrificial line portion on the lower sacrificial layer. An upper spacer is formed by covering a side wall of the upper sacrificial pattern structure. A lower sacrificial pattern structure including a lower sacrificial pad portion and a lower sacrificial line portion is formed by etching the lower sacrificial layer, by using the upper sacrificial pad portion and the upper spacer as an etch mask. A lower spacer layer is formed by covering the lower sacrificial pattern structure. Finally, a lower mask pattern including at least one line mask, at least one bridge mask, and at least one pad mask, is formed by etching the lower spacer layer and the lower sacrificial pattern structure.