Semiconductor transistor devices including alternatively stacked source/drain regions

Abstract

Semiconductor device may include an active region extending in a first direction, channel layers spaced apart from each other in a vertical direction, a gate structure extending on the active region and the channel layers to surround the channel layers and extending in a second direction, and a source/drain region on the active region adjacent to a side of the gate structure and contacting the plurality of channel layers. The source/drain region includes first to sixth epitaxial layers that are sequentially stacked in the vertical direction and have respective first to sixth germanium (Ge) concentrations. The first Ge concentration is lower than the second Ge concentration, the third Ge concentration is lower than the second Ge concentration and the fourth Ge concentration, and the fifth Ge concentration is lower than the fourth Ge concentration and the sixth Ge concentration.