SEMICONDUCTOR DEVICES

A semiconductor device is provided. A semiconductor device includes: a first active pattern spaced apart from a substrate and extending in a first direction; a second active pattern spaced apart further from the substrate than the first active pattern and extending in the first direction; a gate structure on the substrate, the gate structure extending in a second direction crossing the first direction and penetrating the first active pattern and the second active pattern; a first source/drain region on at least one side surface of the gate structure and connected to the first active pattern; a second source/drain region on at least one side surface of the gate structure and connected to the second active pattern; and a buffer layer between the substrate and the first active pattern, the buffer layer containing germanium.