Semiconductor devices

A semiconductor device, comprising:

• a substrate including an active region extending in a first direction;
• a device isolation layer defining the active region on the substrate;
• a gate structure on the substrate, the gate structure extending in a second direction and intersecting the active region;
• and
• a source/drain region on at least one side of the gate structure, wherein
• a first region of the substrate and a second region of the substrate are sequentially disposed in the second direction from a first end of the gate structure in the second direction, and
• an upper surface of the device isolation layer on the first region has a protrusion corresponding to the gate structure, and
• the device isolation layer on the second region has a flat upper surface.

A semiconductor device, comprising:

• a substrate including active regions extending in a first direction;
• a device isolation layer on the substrate and defining the active regions;
• gate structures on the substrate, the gate structures intersecting the active regions and extending in a second direction;
• a plurality of channel layers on the active regions and surrounded by the gate structure, the plurality of channel layer being spaced apart from each other in a third direction, the third direction perpendicular to an upper surface of the substrate;
• and
• source/drain regions in recessed regions of the active regions at both sides of the gate structures, and the source/drain regions being connected to the plurality of channel layers, wherein
• among the active regions, an upper surface of an active region closest to ends of the gate structures in the second direction has a step portion between the gate structures.