A method for fabricating a semiconductor device includes forming a first gate stack over a first fin feature and second gate stack over a second fin feature, removing the first gate stack to form a first gate trench that exposes the first fin structure, removing the second gate stack to form a second gate trench that exposes the second fin feature, performing an annealing process to change a composition of a portion of the first fin feature and forming a first high-k/metal gate (HK/MG) within the first gate trench over the portion of the first fin feature and a second HK/MG within the second gate trench over the second fin feature. Therefore the first HK/MG is formed with a first threshold voltage and the second HK/MG is formed with a second threshold voltage, which is different than the first threshold voltage.