Semiconductor device

A semiconductor device comprising:

• active regions extending on a substrate in a first direction;
• gate structures intersecting the active regions and extending on the substrate in a second direction;
• source/drain regions in recess regions in which the active regions are recessed, on both sides of each of the gate structures;
• and
• contact plugs connected to the source/drain regions,
• wherein each of the source/drain regions includes first and second epitaxial layers sequentially stacked on the active regions in the recess regions in a third direction perpendicular to an upper surface of the substrate, respectively, and
• wherein ratios of the first epitaxial layer thickness in the third direction to the second epitaxial layer thickness in the third direction are different in different ones of the source/drain regions.

A semiconductor device comprising:

• active regions extending on a substrate in a first direction;
• gate structures intersecting the active regions and extending on the substrate in a second direction;
• a plurality of channel layers spaced apart from each other in a third direction, perpendicular to an upper surface of the substrate, on the active regions and surrounded in the second and third directions by the gate structures;
• and
• source/drain regions in recess regions in which the active regions are recessed on at least one side of each of the gate structures,
• wherein each of the source/drain regions includes first and second epitaxial layers sequentially stacked on the active regions in the recess regions in the third direction, respectively,
• wherein the source/drain regions include a first source/drain region in which the second epitaxial layer is at a maximum first depth and a second source/drain region in which the second epitaxial layer is at a maximum second depth different from the maximum first depth, and
• wherein the sums of thicknesses of the first and second epitaxial layers in the third direction in the first and second source/drain regions are substantially equal.