Provided is a semiconductor device including a lower electrode, an upper electrode isolated from direct contact with the lower electrode, and a dielectric layer between the lower electrode and the upper electrode, the dielectric layer comprising a first metal oxide area, a second metal oxide area, and a third metal oxide area. The third metal oxide area is between the first metal oxide area and the second metal oxide area, and includes boron and one or more metal elements selected from aluminum (Al), magnesium (Mg), silicon (Si), or beryllium (Be). In the third metal oxide area, a content of boron (B) is less than or equal to a content of the metal elements of Al, Mg, Si, and/or Be.