In an embodiment, a semiconductor device includes a galvanically isolated signal transfer coupler comprising a contact pad. The contact pad includes a metallic base layer (93), a first isolation layer arranged on peripheral regions of the metallic base layer (93) and having a first opening exposing a portion of the metallic base layer (93), a metallic diffusion barrier layer (97) arranged on the metallic base layer (93). The metallic diffusion barrier layer (97) includes a first portion and a second portion, wherein the second portion of the metallic diffusion barrier layer (97) is arranged in the first opening in the first isolation layer (102) and the first portion of the metallic diffusion barrier layer (97) extends onto a surface of the first isolation layer (102) adjacent the first opening. The first portion has a first surface and a second surface opposing the first surface. The first surface includes a curved surface at the periphery. The first portion extends in a transverse plane and has a width. The second portion protrudes from the second surface intermediate the width of the first portion.