A method of fabricating semiconductor devices includes sequentially forming a gate layer and a mandrel layer on a substrate, forming a first photoresist on the mandrel layer, forming a mandrel pattern by at least partially removing the mandrel layer using the first photoresist as a mask, forming a spacer pattern that comprises a first mandrel spacer located on a side of a first mandrel included in the mandrel pattern and a second mandrel spacer located on the other side of the first mandrel, forming a sacrificial layer that covers the first and second mandrel spacers after removing the mandrel pattern, forming a second photoresist including a bridge pattern overlapping parts of the first and second mandrel spacers on the sacrificial layer; and forming a gate pattern by at least partially removing the gate layer using the first and second mandrel spacers and the second photoresist as a mask.