Methods of fabricating semiconductor devices are provided. An interlayer insulating layer is provided on a single crystalline semiconductor substrate. A single crystalline semiconductor plug is provided that extends through the interlayer insulating layer and a molding layer pattern is provided on the semiconductor substrate and the single crystalline semiconductor plug. The molding layer pattern defines an opening therein that at least partially exposes a portion of the single crystalline semiconductor plug. A single crystalline semiconductor epitaxial pattern is provided on the exposed portion of single crystalline semiconductor plug using a selective epitaxial growth technique that uses the exposed portion of the single crystalline semiconductor plug as a seed layer. A single crystalline semiconductor region is provided in the opening. The single crystalline semiconductor region includes at least a portion of the single crystalline semiconductor epitaxial pattern.