A submount for an electronic device includes an electrically insulating substrate including first and second surfaces and having a thickness between the first and second surfaces, a thermally conductive pad on the first surface of the substrate, and a thermally conductive via extending from the first surface of the substrate toward the second surface of the substrate and having a length that is less than the thickness of the substrate. The thermally conductive via has a higher thermal conductivity than a thermal conductivity of the substrate. Methods of forming submounts are also disclosed.