Semiconductor devices

A semiconductor device comprising:

• channels at a plurality of levels, respectively, the channels spaced apart from each other in a vertical direction on an upper surface of a substrate;
• a gate structure on the substrate, the gate structure at least partially surrounding a surface of each of the channels and extending in a first direction substantially parallel to the upper surface of the substrate, and the gate structure comprising:
• an upper portion on an uppermost one of the channels and overlapping the channels in the vertical direction;
• and
• a lower portion between the channels and between the substrate and a lowermost one of the channels, and overlapping the channels in the vertical direction;
• a first spacer on each of opposite sidewalls of the upper portion of the gate structure in a second direction substantially parallel to the upper surface of the substrate and substantially perpendicular to the first direction;
• a second spacer on each of opposite sidewalls of the lower portion of the gate structure in the second direction, the second spacer having a horseshoe shape convex toward a central portion of the lower portion of the gate structure in the second direction;
• and
• a source/drain layer at each of opposite sides of the gate structure in the second direction, the source/drain layer being connected to the channels,
• wherein a length of the upper portion of the gate structure in the second direction is greater than a minimum value of a length of the lower portion of the gate structure in the second direction.

A semiconductor device comprising:

• channels at a plurality of levels, respectively, the channels spaced apart from each other in a vertical direction on an upper surface of a substrate;
• a gate structure on the substrate, the gate structure at least partially surrounding a surface of each of the channels and extending in a first direction substantially parallel to the upper surface of the substrate;
• and
• a source/drain layer at each of opposite sides of the gate structure in a second direction substantially parallel to the upper surface of the substrate and substantially perpendicular to the first direction, the source/drain layer being connected to sidewalls of the channels,
• wherein a length of a first portion of the gate structure in the second direction increases from a first height toward the upper surface of the substrate,
• the first portion of the gate structure does not overlap the channels in the vertical direction but closes thereto, and
• the first height is a height of an upper surface of an uppermost one of the channels from the upper surface of the substrate.