A device (10′) for welding components by ultrasound. The device (10′) comprises a sonotrode (11′) having a sonotrode head (12′), which can be excited by a vibration generator to produce torsion vibrations with respect to a torsion axis (T). At least one welding surface (14′) is arranged on the peripheral side on the sonotrode head (12′) with respect to the torsion axis (T). The device (10′) also comprises a support device (15′) which supports the sonotrode head (11′) in a support area (16′), which contains a vibration node of the sonotrode head (12′). The support area (16′) and the welding surface (14′) at least partially extend along a common plane (E) which extends perpendicular to the torsion axis (T). A device (10′) for welding components by ultrasound by using a temperature control device are also disclosed.