A semiconductor device is disclosed, which relates to a three-dimensional (3D) semiconductor memory device. The semiconductor device includes a first connection pattern, a bit line disposed over the first connection pattern in a vertical direction, and a bit-line contact pad, disposed in a first layer between the bit line and the first connection pattern to electrically couple the bit line to the first connection pattern so that the bit-line contact pad, and formed as an island when viewed along the vertical direction.