SEMICONDUCTOR DEVICE

A semiconductor device includes a substrate, lower electrodes on the substrate, a dielectric layer covering the lower electrodes, and an upper electrode covering the dielectric layer. The dielectric layer includes a first region in contact with the lower electrodes, a second region in contact with the upper electrode, and a third region between the first and second regions. The third region includes a first insertion layer including a first oxide including a first metal having a first valence and a second oxide including a second metal having a second valence different from the first valence. A thickness of the dielectric layer is about 40 Å to about 60 Å. A thickness of the first insertion layer is about 3 Å to about 10 Å. A ratio of the second metal to total elements in the dielectric layer is about 5 at % to about 15 at %.