A semiconductor device and a method of manufacturing the same, the semiconductor device including a substrate; an insulating layer on the substrate, the insulating layer including a first trench and asecond trench therein, the second trench having an aspect ratio that is smaller than an aspect ratio of the first trench; a barrier layer in the first trench and the second trench; a seed layer on the barrier layer in the first trench and the second trench; a first bulk layer on the seed layer and filled in the first trench; and a second bulk layer on the seed layer and filled in the second trench, wherein an average grain size of the second bulk layer is larger than an average grain size of the first bulk layer.