A semiconductor structure, comprising: a Group III-N semiconductor layer; a source electrode structure (18 1 -18 2) and a drain electrode (22 1 -22 3) structure in Ohmic contact with the Group III-N semiconductor layer; a gate electrode structure (14 1 -14 4), disposed between the source electrode structure and the drain electrode structure, in contact with the Group III-N semiconductor layer; and wherein the source electrode structure, drain electrode structure and gate electrode structure comprising: an electrical contact structure (42 1 -42 7, 14 GC) and an electrode contact (54 1 -54 11) on the electrical contact structure, each electrode contact being of the same material, wherein each one of the electrode contacts (54 1 -54 11) is a gold-free electrically conductive material, and wherein each of the electrode contacts (54 1 -54 11) includes an upper layer of copper having the bottom and sides lined with an adhesion and copper diffusion barrier layer; wherein electrical contact structures of the source electrode structure and drain electrode structure each include: a gold-free Ohmic contact structure, having a bottom layer of titanium or tantalum; a layer of aluminum or Si doped aluminum, Al 1-x Si x, on the bottom layer, where the Si doping, x, is ≤ 0.05; and a top metal layer; and a gold-free electrically conductive etch stop layer (42 ES) disposed on the Ohmic contact structure, wherein the etch stop layer (42 ES) is nickel or molybdenum or platinum. a Group III-N semiconductor layer; a source electrode structure (18 1 -18 2) and a drain electrode (22 1 -22 3) structure in Ohmic contact with the Group III-N semiconductor layer; a gate electrode structure (14 1 -14 4), disposed between the source electrode structure and the drain electrode structure, in contact with the Group III-N semiconductor layer; and wherein the source electrode structure, drain electrode structure and gate electrode structure comprising: an electrical contact structure (42 1 -42 7, 14 GC) and an electrode contact (54 1 -54 11) on the electrical contact structure, each electrode contact being of the same material, wherein each one of the electrode contacts (54 1 -54 11) is a gold-free electrically conductive material, and wherein each of the electrode contacts (54 1 -54 11) includes an upper layer of copper having the bottom and sides lined with an adhesion and copper diffusion barrier layer; wherein electrical contact structures of the source electrode structure and drain electrode structure each include: a gold-free Ohmic contact structure, having a bottom layer of titanium or tantalum; a layer of aluminum or Si doped aluminum, Al 1-x Si x, on the bottom layer, where the Si doping, x, is ≤ 0.05; and a top metal layer; and a gold-free electrically conductive etch stop layer (42 ES) disposed on the Ohmic contact structure, wherein the etch stop layer (42 ES) is nickel or molybdenum or platinum. a gold-free Ohmic contact structure, having a bottom layer of titanium or tantalum; a layer of aluminum or Si doped aluminum, Al 1-x Si x, on the bottom layer, where the Si doping, x, is ≤ 0.05; and a top metal layer; and a gold-free electrically conductive etch stop layer (42 ES) disposed on the Ohmic contact structure, wherein the etch stop layer (42 ES) is nickel or molybdenum or platinum.