Abstract: The disclosure provides a method for fabricating a semiconductor device, in which a core device of the semiconductor device employs a stacked nanowires or nanosheets structure, and an input/output device of the semiconductor device employs FinFET structure. The disclosure also provides a FinFET with an input/output device compatible with the stacked nanowires or nanosheets. The solution of the disclosure solves the problem that if the input/output device employs stacked nanowires or nanosheets device, it is difficult to fill a metal gate between two nanowires or nanosheets due to the thicker dielectric layer, and even if the metal gate is filled partially, the electrical performance of the input/output device is still poor.