A semiconductor device includes a layer having a semiconductive material. The layer includes an outwardly-protruding fin structure. An isolation structure is disposed over the layer but not over the fin structure. A first spacer and a second spacer are each disposed over the isolation structure and on sidewalls of the fin structure. The first spacer is disposed on a first sidewall of the fin structure. The second spacer is disposed on a second sidewall of the fin structure opposite the first sidewall. The second spacer is substantially taller than the first spacer. An epi-layer is grown on the fin structure. The epi-layer protrudes laterally. A lateral protrusion of the epi-layer is asymmetrical with respect to the first side and the second side.