A strained-channel semiconductor structure and method of fabricating the same. The strained-channel semiconductor structure comprises a substrate composed of a first semiconductor material with a first natural lattice constant. A channel region is disposed in the substrate and a gate stack is disposed over the strained channel region. A pair of source/drain regions are oppositely disposed in the substrate adjacent to the channel region, wherein each of the source/drain regions comprises a lattice-mismatched zone comprising a second semiconductor material with a second natural lattice constant rather than the first natural lattice constant, an inner side and an outer side corresponding to the gate stack, and at least one outer sides laterally contacts the first semiconductor material of the substrate.