Methods of forming transistor devices are provided. A method of forming a transistor device includes providing a nanosheet stack that includes a plurality of nanosheets on a substrate. A sacrificial layer is between the nanosheet stack and the substrate. The method includes removing the sacrificial layer to form an opening between the nanosheet stack and the substrate. The method includes forming a gate spacer and an isolation region by forming an insulating material on the nanosheet stack and in the opening, respectively. Related transistor devices are also provided.