Disclosed are semiconductor devices and their fabrication methods. The semiconductor device comprises a substrate including a peripheral block and cell blocks each including a cell center region, a cell edge region, and a cell middle region, and bit lines extending on each cell block in a first direction. The bit lines include center bit lines, middle bit lines, and edge bit lines. The bit line has first and second lateral surfaces opposite to each other in a second direction. The first lateral surface straightly extends along the first direction on the cell center region, the cell middle region, and the cell edge region. The second lateral surface straightly extends along the first direction on the cell center region and the cell edge region, and the second lateral surface extends along a third direction, that intersects the first direction and the second direction, on the cell middle region.