Three-dimensional semiconductor memory devices and methods of fabricating the same. The device may include first, second and third conductive lines disposed at different vertical levels to define two intersections, and two memory cells disposed at the two intersections, respectively. The first and second conductive lines may extend parallel to each other, and the third conductive line may extend to cross the first and second conductive lines. The first and second conductive lines can be alternatingly arranged along the length of third conductive line in vertical sectional view, and the third conductive line may be spaced vertically apart from the first and second conductive lines.