The invention relates to a method for producing a solid electrolytic capacitor with excellent LC value, comprising sequentially stacking a dielectric oxide film, a semiconductor layer and an electrode layer on a sintered body of conductive powder to which an anode lead is connected and then encapsulating the whole with an outer jacket resin, wherein surface area of a cathode plate used in forming the semiconductor layer on the dielectric oxide film by applying current between the conductor having the dielectric oxide film thereon used as anode and the cathode plate provided in electrolysis solution is made larger by 10 times or more than its apparent surface area to thereby efficiently form the semiconductor layer, a capacitor produced by the method, and electronic circuits and electronic devices using the capacitor.