Semiconductor device

A semiconductor device includes: an active region extending in a first direction on a substrate; a plurality of semiconductor layers spaced apart from each other in a vertical direction on the active region, the plurality of semiconductor layers including a lower semiconductor layer and an upper semiconductor layer; a gate structure extending in a second direction on the substrate to intersect the active region and the plurality of semiconductor layers; and a source/drain region on the active region and contacting the plurality of semiconductor layers. The source/drain region includes a first epitaxial layer including a first layer on a side surface of the lower semiconductor layer and a second layer provided on and contacting the active region, and a second epitaxial layer contacting a side surface of the upper semiconductor layer in a first direction, and the first layer is between the second epitaxial layer and a side surface of the lower semiconductor layer. 一种半导体器件包括：有源区，在基板上在第一方向上延伸；多个半导体层，在有源区上在垂直方向上彼此