Provided are a dielectric, a capacitor and a semiconductor device that include the dielectric, and a method of preparing the dielectric, the dielectric including: a composition represented by Formula 1; and an oxide including a perovskite type crystal structure having a polar space group or a non-polar space group other than a Pbnm space group: AxByO3-δ   wherein, in Formula 1, A is a monovalent, divalent, or trivalent cation, B is a trivalent, tetravalent, or pentavalent cation, and 0.5≤x≤1.5, 0.5≤y≤1.5, and 0≤δ≤0.5.