A package for a high-frequency device, characterized in that high-precision electrodes are provided on both sides of a fired ceramic substrate, a cured sealing auxiliary layer of an organic polymer material or an inorganic material is formed along the periphery, a device is mounted on the substrate surrounded by the sealing auxiliary layer and electrically connected to the electrodes, and a cap member is bonded to the sealing auxiliary layer with an adhesive gas-tightly. The package can be manufactured and inspected at low cost and used in high-frequency range including the millimeter-wave band (20 100GHz).
