A semiconductor device, comprising: a galvanically isolated signal transfer coupler comprising a contact pad (91; 120), wherein the contact pad comprises: a metallic base layer; a metallic diffusion barrier layer arranged on the metallic base layer, and a metallic wire bondable layer arranged on the metallic diffusion barrier layer, wherein the metallic diffusion barrier layer comprises a first portion having a first surface and a second surface opposing the first surface, the first surface of the first portion comprising a curved surface at the periphery, the first portion extending in a transverse plane and having a width, a second portion protruding from the second surface intermediate the width of the first portion, a first isolation layer arranged on peripheral regions of the metallic base layer and having a first opening exposing a portion of the metallic base layer, wherein the second portion of the metallic diffusion barrier layer is arranged in the first opening in the first isolation layer and the first portion of the metallic diffusion barrier layer extends onto a surface of the first isolation layer adjacent the first opening, a second isolation layer arranged on peripheral regions of the metallic wire bondable layer and comprising a second opening exposing a portion of the metallic wire bondable layer, a metallic passivation layer on the metallic wire bondable layer, wherein the metallic passivation layer is arranged in and bounded by the second opening. a galvanically isolated signal transfer coupler comprising a contact pad (91; 120), wherein the contact pad comprises: a metallic base layer; a metallic diffusion barrier layer arranged on the metallic base layer, and a metallic wire bondable layer arranged on the metallic diffusion barrier layer, wherein the metallic diffusion barrier layer comprises a first portion having a first surface and a second surface opposing the first surface, the first surface of the first portion comprising a curved surface at the periphery, the first portion extending in a transverse plane and having a width, a second portion protruding from the second surface intermediate the width of the first portion, a first isolation layer arranged on peripheral regions of the metallic base layer and having a first opening exposing a portion of the metallic base layer, wherein the second portion of the metallic diffusion barrier layer is arranged in the first opening in the first isolation layer and the first portion of the metallic diffusion barrier layer extends onto a surface of the first isolation layer adjacent the first opening, a second isolation layer arranged on peripheral regions of the metallic wire bondable layer and comprising a second opening exposing a portion of the metallic wire bondable layer, a metallic passivation layer on the metallic wire bondable layer, wherein the metallic passivation layer is arranged in and bounded by the second opening. a metallic base layer; a metallic diffusion barrier layer arranged on the metallic base layer, and a metallic wire bondable layer arranged on the metallic diffusion barrier layer, wherein the metallic diffusion barrier layer comprises a first portion having a first surface and a second surface opposing the first surface, the first surface of the first portion comprising a curved surface at the periphery, the first portion extending in a transverse plane and having a width, a second portion protruding from the second surface intermediate the width of the first portion, a first isolation layer arranged on peripheral regions of the metallic base layer and having a first opening exposing a portion of the metallic base layer, wherein the second portion of the metallic diffusion barrier layer is arranged in the first opening in the first isolation layer and the first portion of the metallic diffusion barrier layer extends onto a surface of the first isolation layer adjacent the first opening, a second isolation layer arranged on peripheral regions of the metallic wire bondable layer and comprising a second opening exposing a portion of the metallic wire bondable layer, a metallic passivation layer on the metallic wire bondable layer, wherein the metallic passivation layer is arranged in and bounded by the second opening.