A semiconductor device includes an active region extending in a first direction, a gate structure extending in a second direction, a source/drain region on the active region, a first contact structure connected to the source/drain region, and a second contact structure connected to the first contact structure. The second contact structure includes a first layer including a first grain and a second layer including second grains on the first layer. Within the first layer, a maximum vertical distance between a lowermost end of the first grain and an uppermost end of the first grain is equal to a vertical distance between a lowermost end of the first layer and an uppermost end of the first layer. A size of the first grain is greater than a size of each of the second grains. A width of the first layer is greater than a width of the first contact structure.