Semiconductor device

A semiconductor device, comprising:

• a substrate;
• and
• a first transistor disposed on the substrate, the first transistor comprising:
• a first semiconductor channel structure, wherein the first semiconductor channel structure comprises:
• first horizontal portions stacked in a vertical direction and separated from one another, wherein each of the first horizontal portions is elongated in a horizontal direction;
• and
• a first vertical portion elongated in the vertical direction and connected with the first horizontal portions, wherein a material composition of the first vertical portion is identical to a material composition of each of the first horizontal portions;
• two first source/drain structures disposed at two opposite sides of each of the first horizontal portions in the horizontal direction respectively, wherein the two first source/drain structures are connected with the first horizontal portions;
• and
• a first gate structure encompassing the first horizontal portions and the first vertical portion of the first semiconductor channel structure, wherein a part of the first gate structure is disposed between the first vertical portion of the first semiconductor channel structure and the substrate in the vertical direction.