Three-dimensional semiconductor device

Provided are a three-dimensional semiconductor device and a method of fabricating the same. The three-dimensional semiconductor device may include a mold structure for providing gap regions and an interconnection structure including a plurality of interconnection patterns disposed in the gap regions. The mold structure may include interlayer molds defining upper surfaces and lower surfaces of the interconnection patterns and sidewall molds defining sidewalls of the interconnection patterns below the interlayer molds.