Semiconductor device and fabrication method thereof

A fabrication method of a semiconductor device, comprising:

• providing a substrate, having a plurality of fins on a surface of the substrate;
• forming an initial gate structure across the plurality of fins, wherein the initial gate structure covers a portion of a top surface and side wall surfaces of the plurality of fins, the initial gate structure includes an initial first region and an initial second region on the initial first region, a bottom boundary of the initial second region is higher than the top surface of the plurality of fins, and a size of the initial first region in an extending direction of the plurality of fins is larger than a size of the initial second region in the extending direction of the plurality of fins;
• and
• performing a first etching process on sidewalls of the initial gate structure to form a gate structure;
• wherein the gate structure includes a first region formed by etching the initial first region, and a second region formed by etching the initial second region, and a size of the first region in the extending direction of the plurality of fins is smaller than a size of the second region in the extending direction of the plurality of fins.