US Patent 7822090 Semiconductor device

A semiconductor device includes an optical semiconductor element, a package including a base made of a metal for mounting the optical semiconductor element, and a cap for encapsulating the optical semiconductor element and a gas by covering the package and the optical semiconductor element. The gas encapsulated with the package has an oxygen concentration not less than 15% and less than 30% and has a dew-point not less than −15° C. and not more than −5° C.