3d fet devices and methods for manufacturing the same

A semiconductor device, comprising:

• a first transistor comprising:
• a first semiconductor structure vertically extending away and separated from the semiconductor substrate;
• a first source/drain structure surrounding the first semiconductor structure;
• a first gate structure surrounding the first semiconductor structure and disposed above the first source/drain structure;
• and
• a second source/drain structure surrounding the first semiconductor structure and disposed above the first gate structure;
• and
• a second transistor disposed above a second semiconductor structure that vertically extends and is in contact with the semiconductor substrate, and comprising:
• a third semiconductor structure laterally extending;
• a third source/drain structure in contact with a first end of the third semiconductor structure;
• a second gate structure surrounding the third semiconductor structure;
• and
• a fourth source/drain structure in contact with a second end of the third semiconductor structure.

A method for fabricating semiconductor devices, comprising:

• epitaxially growing a first semiconductor structure and a second semiconductor structure from a semiconductor substrate, wherein the first and second semiconductor structures each extend in a vertical direction with a same height;
• replacing a bottom portion of the first semiconductor structure with a first dielectric structure;
• forming a first transistor around the first semiconductor structure;
• epitaxially growing first, second, third, and fourth semiconductor layers over the second semiconductor structure;
• replacing the first semiconductor layer with a second dielectric structure;
• and
• forming a second transistor above the second dielectric structure.