A semiconductor device is provided. The semiconductor device includes first channel nanostructures in a first device region, second channel nanostructures in a second device region, a dielectric fin at a boundary between the first device region and the second device region, a high-k dielectric layer surrounding each of the first channel nanostructures and each of the second channel nanostructures and over the dielectric fin, a first work function layer surrounding each of the first channel nanostructures and over the high-k dielectric layer and a second work function layer surrounding each of the second channel nanostructures and over the high-k dielectric layer and the first work function layer. The first work functional layer fully fills spaces between the first channel nanostructures and has an edge located above the dielectric fin. The second work functional layer fully fills spaces between the second channel nanostructures.