A device for welding rod-shaped electrical conductors and a sonotrode for such includes a compression space for receiving two connection regions of the conductors to be connected, said connection regions extending in a first axial direction (x-axis), the compression space being defined by a working surface of a sonotrode, which transmits ultrasonic vibrations, and a counterface of an anvil at two opposite sides in a second axial direction (z-axis) and by a boundary surface of a slider element, displaceable in the second axial direction (z-axis), and a boundary surface of a boundary element on two opposite sides in a third axial direction (y-axis). In a special contact zone, which is a section of the working surface of the sonotrode and serves to subject at least one connection region to ultrasonic vibrations, the working surface has a surface configuration that differs from a contact zone formed by the remaining working surface.