  We present a Josephson junction based on a Ge-Si core-shell nanowire with
transparent superconducting Al contacts, a building block which could be of
considerable interest for investigating Majorana bound states, superconducting
qubits and Andreev (spin) qubits. We demonstrate the dc Josephson effect in the
form of a finite supercurrent through the junction, and establish the ac
Josephson effect by showing up to 23 Shapiro steps. We observe multiple Andreev
reflections up to the sixth order, indicating that charges can scatter
elastically many times inside our junction, and that our interfaces between
superconductor and semiconductor are transparent and have low disorder.
