A microwave circuit package includes a metallic base plate on which are mounted a plurality of monolithic microwave integrated circuits (MMICs) and a spacer, made of a dielectric material, separating the MMICs from each other, and the MMICs and spacer are sealed in the package. The provision of the spacer substantially reduces the volume of the interior space of the package. A dielectric substrate having generally the same height as substrates of the MMICs may also be mounted on the metallic base plate, and a strip conductor may be provided on the dielectric substrate so as to form a microstrip line thereon.