In a cell array region of a NOR-type mask ROM device and a fabricating method therefor, following formation of a plurality of word lines parallel to one another on a semiconductor substrate, a plurality of sub-bit lines intersecting the top portion of the plurality of word lines at right angles are formed. Trench regions are formed on the semiconductor substrate exposed by the plurality of word lines and the plurality of sub-bit lines. An interlayer insulating layer is formed on the entire surface of the resulting material, and a plurality of bit lines which are parallel to one another are formed on the interlayer insulating layer.