Semiconductor devices

A semiconductor device, comprising:

• an active region extending in a first direction on a substrate;
• a plurality of channel layers on the active region, the plurality of channel layers being spaced apart from each other in a third direction perpendicular to the first direction;
• a gate structure on the substrate intersecting the active region and the plurality of channel layers and extending in a second direction, the gate structure surrounding the plurality of channel layers;
• and
• a source/drain region on the active region and at least one side of the gate structure, the source/drain region being in contact with the plurality of channel layers,
• wherein the source/drain region includes:
• a plurality of first epitaxial layers on side surfaces of the plurality of channel layers in the first direction, each of the plurality of first epitaxial layers including first impurities of a first conductivity type;
• and
• a second epitaxial layer filling a space between the plurality of first epitaxial layers and including second impurities of the first conductivity type.

A semiconductor device, comprising:

• an active structure extending in a first direction on a substrate and having channel regions;
• gate structures intersecting the channel regions and extending in a second direction;
• and
• source/drain regions on both sides of the gate structures,
• wherein each of the source/drain regions includes:
• a first semiconductor layer including first impurities in a first concentration;
• and
• a plurality of second semiconductor layers separated from each other to be in contact with the channel regions, respectively, between the first semiconductor layer and the channel regions, and including second impurities in a second concentration that is lower than the first concentration.