Method of fabricating flat-cell mask read-only memory devices

According to embodiments of the invention, a first gate insulating pattern and a mask pattern are sequentially stacked on a semiconductor substrate. Subsequently an impurity region is formed in the semiconductor substrate. Next, the mask pattern is removed to expose the first gate insulating pattern and a second gate insulating layer is formed on the entire surface thereof. The mask pattern is preferably formed of an anti-reflecting pattern and a photoresist pattern that are sequentially stacked. The anti-reflecting pattern is preferably formed of a material layer without etching selectivity with respect to the photoresist pattern. For this, the anti-reflecting pattern is preferably formed of organic materials including hydrocarbonic compounds. In addition, removing a mask pattern is performed with an etch recipe having an etch selectivity with respect to the first gate insulating pattern.