Semiconductor devices and method of forming the same are provided. In one embodiment, a semiconductor device includes a first transistor and a second transistor. The first transistor includes two first source/drain features and a first number of nanostructures that are stacked vertically one over another and extend lengthwise between the two first source/drain features. The second transistor includes two second source/drain features and a second number of nanostructures that are stacked vertically one over another and extend lengthwise between the two second source/drain features.