Semiconductor devices including empty spaces and methods of forming the semiconductor devices are provided. The semiconductor devices may include first and second line structures extending in a direction on a substrate, an insulating isolation pattern between the first and second line structures and a conductive structure between the first and second line structures and next to the insulating isolation pattern along the direction. The semiconductor devices may also include an empty space including a first portion between the first line structure and the conductive structure and a second portion between the first line structure and the insulating isolation pattern. The first portion of the empty space may have a height different from a height of the second portion of the empty space.