Semiconductor device and manufacturing method thereof

A semiconductor device includes first and second transistors each having a high-k metal gate disposed over a respective channel region of the transistors. The semiconductor device further includes first and second dielectric features in physical contact with an end of the respective high-k metal gates. The first and second transistors are of a same conductivity type. The two high-k metal gates have a same number of material layers. The first transistor's threshold voltage is different from the second transistor's threshold voltage, and at least one of following is true: the two high-k metal gates have different widths, the first and second dielectric features have different distances from respective channel regions of the two transistors, and the first and second dielectric features have different dimensions.