Method for forming semiconductor device

A semiconductor device and a method of forming the same are provided. The method includes forming a fin extending from a substrate and forming a gate dielectric layer along a top surface and sidewalls of the fin. The first thickness of the gate dielectric layer along the top surface of the fin is greater than the second thickness of the gate dielectric layer along the sidewalls of the fin. 提供半导体装置与其形成方法。方法包括形成鳍状物，且鳍状物自基板延伸；以及沿着鳍状物的上表面与侧壁形成栅极介电层。沿着鳍状物的上表面的栅极介电层的第一厚度，大于沿着鳍状物的侧壁的栅极介电层的第二厚度。