A semiconductor device includes an insulating film provided over a semiconductor substrate, a conductive plug buried in the insulating film, an underlying conductive film which is provided on the conductive plug and on the insulating film and which has a flat upper surface, and a ferroelectric capacitor provided on the underlying conductive film. At least in a region on the conductive plug, the concentration of nitrogen in the underlying conductive film gradually decreases from the upper surface to the inside.