A microwave device includes a first substrate having a first surface, a first metal layer, a second substrate having a second surface corresponding to the first substrate, a second metal layer, a sealing element, a modulation material, and a fill material. The first metal layer is disposed on the first surface, and the first metal layer includes openings. The second metal layer is disposed on the second surface. The second metal layer includes electrodes corresponding to the openings. The sealing element is located between the first substrate and the second substrate. An active zone is formed by a space between the sealing element, the first substrate, and the second substrate. The modulation material is filled within the active area. The fill material is disposed in the active area. The thickness of the fill material is greater than 0.3 μm, and less than the thickness of the sealing element.