To provide a semiconductor device capable of improving accuracy in finishing a hole in which a conductive plug right under a capacitor, and a manufacturing method of such a semiconductor device comprising the following steps: a step of forming first and second conductive plugs 32a, 32b in first and second holes 11a, 11b in a first insulating film 11; a step of forming a first opening 14a in an oxidation preventing insulating film 14; a step of forming an auxiliary conductive plug 36a in the first opening 14a; a step of forming a capacitor Q on the auxiliary conductive plug 36a; a step of forming third and fourth holes 41a, 41b in a second insulating film 41 covering the capacitor Q; a step of forming the second opening 14b in the oxidation preventing insulating film 14 under the fourth hole 41b; a step of forming a third conductive plug 47a in the third hole 41a; and a step of forming a fourth conductive plug 47b in the third hole 41a.