Fin field effect transistors having vertically stacked nano-sheet

A structure, comprising:

• a fin field effect transistor (finFET) on a substrate, wherein the finFET comprises:
• a fin structure on the substrate;
• a shallow trench isolation (STI) region adjacent to the fin structure and having a non-planar top surface;
• and
• a first gate structure over surfaces of the fin structure;
• and
• a nano-sheet transistor on the substrate, wherein the nano-sheet transistor comprises:
• a vertical structure on the substrate;
• a plurality of nano-sheet layers on the vertical structure;
• and
• a second gate structure surrounding each of the plurality of nano-sheet layers.

A structure, comprising:

• a fin field effect transistor (finFET) on a substrate and comprising a fin channel region having a first channel length;
• and
• a gate-all-around field effect transistor (GAAFET) on the substrate and comprising:
• a buffer region;
• a nano-sheet channel region on the buffer region and having a second channel length different from the first channel length;
• and
• a shallow trench isolation region adjacent to the buffer region and having a non-planar top surface.