A semiconductor device structure, along with methods of forming such, are described. The structure includes a plurality of semiconductor layers having a first group of semiconductor layers, a second group of semiconductor layers disposed over and aligned with the first group of semiconductor layers, and a third group of semiconductor layers disposed over and aligned with the second group of semiconductor layers. The structure further includes a first source/drain epitaxial feature in contact with a first number of semiconductor layers of the first group of semiconductor layers and a second source/drain epitaxial feature in contact with a second number of semiconductor layers of the third group of semiconductor layers. The first number of semiconductor layers of the first group of semiconductor layers is different from the second number of semiconductor layers of the third group of semiconductor layers.