Apparatus comprising: a semiconductor device comprising an integrated circuit and a plurality of external radiating elements at a surface of the device, the radiating elements including at least one transmit element and at least one receive element; and a test apparatus configured to test the semiconductor device, the test apparatus comprising: a surface for placing against said surface of the device; and at least one waveguide, wherein each waveguide extends through the test apparatus and is configured to route electromagnetic radiation transmitted by one of said transmit elements of the device to one of the receive elements of the device, wherein each waveguide comprises a plurality of waveguide openings for coupling electromagnetically to corresponding radiating elements of the plurality of radiating elements located at the surface of the device, wherein a spacing between the waveguide openings of each waveguide of the test apparatus is larger than, or smaller than a spacing between the corresponding radiating elements of the device, wherein at least one of the waveguides is configured to route electromagnetic radiation transmitted by one of said transmit elements of the device to a plurality of receive elements of the device, characterised in that said at least one of the waveguides comprises: a first branch for conveying electromagnetic radiation transmitted by said transmit element, and a t least two further branches (64B, 64C) coupled to the first branch configured to route said electromagnetic radiation to said plurality of receive element. a semiconductor device comprising an integrated circuit and a plurality of external radiating elements at a surface of the device, the radiating elements including at least one transmit element and at least one receive element; and a test apparatus configured to test the semiconductor device, the test apparatus comprising: a surface for placing against said surface of the device; and at least one waveguide, wherein each waveguide extends through the test apparatus and is configured to route electromagnetic radiation transmitted by one of said transmit elements of the device to one of the receive elements of the device, wherein each waveguide comprises a plurality of waveguide openings for coupling electromagnetically to corresponding radiating elements of the plurality of radiating elements located at the surface of the device, a surface for placing against said surface of the device; and at least one waveguide, wherein each waveguide extends through the test apparatus and is configured to route electromagnetic radiation transmitted by one of said transmit elements of the device to one of the receive elements of the device, wherein each waveguide comprises a plurality of waveguide openings for coupling electromagnetically to corresponding radiating elements of the plurality of radiating elements located at the surface of the device, wherein a spacing between the waveguide openings of each waveguide of the test apparatus is larger than, or smaller than a spacing between the corresponding radiating elements of the device, wherein at least one of the waveguides is configured to route electromagnetic radiation transmitted by one of said transmit elements of the device to a plurality of receive elements of the device, characterised in that said at least one of the waveguides comprises: a first branch for conveying electromagnetic radiation transmitted by said transmit element, and a t least two further branches (64B, 64C) coupled to the first branch configured to route said electromagnetic radiation to said plurality of receive element. a first branch for conveying electromagnetic radiation transmitted by said transmit element, and a t least two further branches (64B, 64C) coupled to the first branch configured to route said electromagnetic radiation to said plurality of receive element.