A method for forming a semiconductor gate structure and a semiconductor gate structure are provided. The method comprises: providing a substrate with a Ge layer as a surface thereof; forming a Sn layer on the Ge layer, in which an interface between the Ge layer and the Sn layer is a GeSn layer; removing the Sn layer to expose the GeSn layer; forming a GeSnO x passivation layer by performing an oxidation treatment for the GeSn layer, or forming a GeSnN or GeSnON passivation layer by performing a passivation treatment for the GeSn layer; and forming a gate stack on the GeSnO x , GeSnN or GeSnON passivation layer.