A method for forming a gate electrode includes: providing a substrate; forming a gate dielectric layer and forming a sacrificial layer, the sacrificial layer including doping ions, a density of the doping ions in the sacrificial layer decreasing with increasing distance from the substrate; forming a hard mask layer; patterning the sacrificial layer and the hard mask layer; removing part of the patterned sacrificial layer by wet etching with the patterned hard mask layer as a mask, to form a dummy gate electrode which has a top width bigger than a bottom width, and removing the patterned hard mask layer; removing the dummy gate electrode and filling a gate trench with gate material to form a gate electrode which has a top width bigger than a bottom width, which facilitates the filling of the gate material and can avoid or reduce cavity forming in the gate material.