Semiconductor device and manufacturing method thereof

A semiconductor device, comprising:

• a semiconductor substrate;
• a first semiconductor channel layer disposed above the semiconductor substrate;
• a second semiconductor channel layer disposed above the semiconductor substrate;
• an isolation structure disposed above the semiconductor substrate, wherein the isolation structure comprises:
• a vertical portion disposed between the first semiconductor channel layer and the second semiconductor channel layer in a horizontal direction;
• a first horizontal portion disposed between the first semiconductor channel layer and the semiconductor substrate in a vertical direction;
• and
• a second horizontal portion disposed between the second semiconductor channel layer and the semiconductor substrate in the vertical direction, wherein the first horizontal portion and the second horizontal portion are connected with the vertical portion;
• a first gate structure disposed above the semiconductor substrate and encompassing the first semiconductor channel layer;
• and
• a second gate structure disposed above the semiconductor substrate and encompassing the second semiconductor channel layer, wherein the first gate structure and the second gate structure are partly disposed above the vertical portion of the isolation structure, and the first gate structure and the second gate structure are connected with each other.