A method for fabricating a thin-film semiconductor device for display according to the present disclosure includes: preparing a glass substrate; forming, above the glass substrate, an undercoat layer including a nitride film; forming a molybdenum metal layer above the undercoat layer; forming a gate electrode from the metal layer by an etching process; forming a gate insulating film above the gate electrode; forming a non-crystalline silicon layer as a non-crystalline semiconductor layer above the gate insulating film; forming a polycrystalline semiconductor layer which is a polysilicon layer by annealing the non-crystalline silicon layer at a temperature in a range from 700° C. to 1400° C.; forming a source electrode and a drain electrode above the polysilicon layer; and performing hydrogen plasma treatment at a stage after the metal layer is formed and before the polysilicon layer is formed, using a radio frequency power in a range from 0.098 W/cm2 to 0.262 W/cm2.