A semiconductor device, and a method of fabrication the same, include selection gate patterns extending in a first direction on a substrate, cell gate patterns extending in parallel in the first direction between the selection gate patterns adjacent to each other, and contact pads connected to first end parts of the cell gate patterns, respectively. An insulating layer covers the selection gate patterns, the cell gate patterns, and the contact pads. The insulating layer includes a void or seam between the contact pads. A filling insulating layer fills the void or seam in the insulating layer.