A stackable semiconductor assembly includes a semiconductor device, a heat spreader, an adhesive, a plated through-hole, first build-up circuitry and second build-up circuitry. The heat spreader includes a bump and a flange. The bump defines a cavity. The semiconductor device is mounted on the bump at the cavity, electrically connected to the first build-up circuitry and thermally connected to the bump. The bump extends into an opening in the adhesive and the flange extends laterally from the bump at the cavity entrance. The first build-up circuitry and the second build-up circuitry extend beyond the semiconductor device in opposite vertical directions. The plated through-hole extends through the adhesive and provides signal routing between the first build-up circuitry and the second build-up circuitry. The heat spreader provides heat dissipation for the semiconductor device.