A semiconductor package has a substrate having a first heat transfer path for transferring heat from an optical functional element to a back surface of the substrate, a first heat dissipation unit dissipating the transferred heat therefrom, a second heat transfer path for transferring heat generated in an internal cavity and heat from a window lid itself to a back surface and/or a side surface of the substrate, a second heat dissipation unit dissipating the transferred heat therefrom. The heat transfer paths extend through the substrate and have thermal vias.