An optical semiconductor hermetic sealing package for accommodating an optical semiconductor element therein, comprising: a frame made of a metal, an insulator, or a composite of metal and insulator; a first bottom plate made of a metal fixed to the frame; a second bottom plate whose Young's modulus is larger than that of the first bottom plate and which is fixed to the surface of the first bottom plate on the opposite side to the frame; and a metal block plate that is fixed to the surface of flanges projecting on both sides of the first bottom plate, on the side of the second bottom plate. The optical semiconductor hermetic sealing package is capable of alleviating warping of the bottom plate and has an even more excellent heat radiating characteristic.