A fin field effect transistor includes a first fin structure and a second fin structures both protruding from a substrate, first and second gate electrodes on the first and second fin structures, respectively, and a gate dielectric layer between each of the first and second fin structures and the first and second gate electrodes, respectively. Each of the first and second fin structures includes a buffer pattern on the substrate, a channel pattern on the buffer pattern, and an etch stop pattern provided between the channel pattern and the substrate. The etch stop pattern includes a material having an etch resistivity greater than that of the buffer pattern.