A method of making a semiconductor device includes forming a first transmission line over a substrate. The method includes forming a second transmission line over the substrate. The method further includes depositing a high-k dielectric material between the first transmission line and the second transmission line, wherein the high-k dielectric material partially covers each of the first transmission line and the second transmission line. The method further includes depositing a dielectric material directly contacting the high-k dielectric material, wherein the dielectric material has a different dielectric constant from the high-k dielectric material, and the dielectric material directly contacts the first transmission line or the second transmission line.