A semiconductor device is provided. The semiconductor device includes a plurality of first semiconductor nanosheets spaced apart from each other and in a p-type device region, and a plurality of second semiconductor nanosheets spaced apart from each other and in an n-type device region. The semiconductor device includes an isolation structure formed at a boundary between the p-type and n-type device regions, and a first hard mask layer formed over the first semiconductor nanosheets. The semiconductor device also includes a second hard mask layer formed over the second semiconductor nanosheets, and a p-type work function layer surrounding each of the first semiconductor nanosheets and the first hard mask layer.