An antenna device includes a first substrate, a second substrate, an antenna layer, and a redistribution layer. The first substrate has a first surface, a second surface opposite to the first surface, and an inclined sidewall adjoining the first and second surfaces. The second substrate is below the first substrate. The first surface of the first substrate faces toward the second substrate. The antenna layer is located on the first surface of the first substrate. The redistribution layer extends from the second surface of the first substrate to the second substrate along the inclined sidewall of the first substrate, and the redistribution layer has a first section in contact with an end of the antenna layer.