Semiconductor device including gate structure and multiple integrated separation structures

A method of manufacturing a semiconductor device, the method comprising:

• forming a sacrificial gate structure;
• forming a first opening penetrating through the sacrificial gate structure;
• forming a first separation structure in a lower region of the first opening;
• removing the sacrificial gate structure to form a gate opening;
• forming a gate structure in the gate opening and on the first separation structure;
• forming a second opening penetrating through the gate structure to expose the first separation structure;
• and
• forming a second separation structure in the second opening.

A method of manufacturing a semiconductor device, the method comprising:

• forming active structures including a plurality of channel layers;
• forming a sacrificial gate structure crossing the active structures;
• forming source/drain regions adjacent to opposite sides of the sacrificial gate structure;
• forming an interlayer insulating layer on the source/drain regions;
• forming a first opening penetrating through the sacrificial gate structure and the interlayer insulating layer;
• forming a first separation structure in the first opening;
• removing the sacrificial gate structure to form a gate opening;
• forming a gate structure in the gate opening and on the first separation structure;
• forming a second opening penetrating through the gate structure to expose the first separation structure;
• and
• forming a second separation structure in the second opening, the second separation structure contacting the first separation structure.