A semiconductor device includes a gate pattern on a substrate, a multi-channel active pattern under the gate pattern to cross the gate pattern and having a first region not overlapping the gate pattern and a second region overlapping the gate pattern, a diffusion layer in the multi-channel active pattern along the outer periphery of the first region and including an impurity having a concentration, and a liner on the multi-channel active pattern, the liner extending on lateral surfaces of the first region and not extending on a top surface of the first region. Related fabrication methods are also described.