Semiconductor packages having a first layer interconnect portion that includes a coaxial interconnect between a die and a package substrate are described. In an example, the package substrate includes a substrate-side coaxial interconnect electrically connected to a signal line. The die is mounted on the package substrate and includes a die-side coaxial interconnect coupled to the substrate-side coaxial interconnect. The coaxial interconnects can be joined by a solder bond between respective central conductors and shield conductors.