A semiconductor device includes a circuit substrate, a semiconductor package, and a metallic cover. The semiconductor package is disposed on the circuit substrate. The metallic cover is disposed over the semiconductor package and over the circuit substrate. The metallic cover comprises a lid and outer flanges. The lid overlies the semiconductor package. The outer flanges are disposed at edges of the lid, are connected with the lid, extend from the lid towards the circuit substrate, and face side surfaces of the semiconductor package. The lid has a first region that is located over the semiconductor package and is thicker than a second region that is located outside a footprint of the semiconductor package.