US Patent 11031502 Semiconductor devices

A semiconductor device includes an active region extending in a first direction on a substrate, channel layers on the active region and spaced apart vertically, a gate structure intersecting the active region and the channel layers, the gate structure extending in a second direction and surrounding the channel layers, and a source/drain region on the active region at a side of the gate structure, the source/drain region contacting the channel layers, the source/drain region including first epitaxial layers having a first composition and including first layers on side surfaces of the channel layers and a second layer on the active region at a lower end of the source/drain region, and a second epitaxial layer having a second composition different from the first composition, the second epitaxial layer being between the first epitaxial layers in the first direction and being between the first epitaxial layers vertically in a third direction.