The present disclosure relates to a semiconductor device with a contact structure and a method for preparing the semiconductor device. The semiconductor device includes a source/drain structure disposed over a semiconductor substrate, and a dielectric layer disposed over the source/drain structure. The semiconductor device also includes a polysilicon stack disposed over the source/drain structure and surrounded by the dielectric layer. The polysilicon stack includes a first polysilicon layer and a second polysilicon layer disposed over the first polysilicon layer. The first polysilicon layer is undoped, and the second polysilicon layer is doped. The semiconductor device further includes a contact structure disposed directly over the polysilicon stack and surrounded by the dielectric layer.