A method of fabricating a non-volatile memory integrated circuit device and a non-volatile memory integrated circuit device fabricated by using the method are provided. A device isolation region is formed in a substrate to define a cell array region and a peripheral circuit region. A plurality of first and second pre-stacked gate structures is formed in the cell array region, and each has a structure in which a lower structure, a conductive pattern and a first sacrificial layer pattern are stacked. Junction regions are formed in the cell array region. Spacers are formed on side walls of the first and second pre-stacked gate structures. A second sacrificial layer pattern filling each space between the second pre-stacked gate structures is formed. The first sacrificial layer pattern is removed from each of the first and second pre-stacked gate structures. A damascene metal layer pattern is formed in each of spaces of the first and second pre-stacked gate structures from which the first sacrificial layer pattern is removed, thus completing first and second stacked gate structures. The second sacrificial layer pattern is removed. A stop layer is formed on top surfaces of the first stacked gate structures, top surfaces and side walls of the second stacked gate structures, and a top surface of the substrate.