The temperature-induced mixed valence transition in EuNi 2 (Si 0.20 Ge 0.80 ) 2 has been investigated by hard X-ray (5940eV) photoemission spectroscopy (HX-PES) for fractured surfaces, with a probing depth larger than 5nm. The Eu 3d core-level states are studied below and above the critical valence transition temperature, T v =80K. The HX-PES spectra at 40 and 120K show the mixed valence transition, with clear changes in the divalent and trivalent Eu 3d chemically shifted features. The Eu 3d HX-PES spectra indicate a mean valence of 2.70±0.03 at 40K which changes to 2.40±0.03 at 120K, in good accordance with the results of bulk Eu III -edge X-ray absorption spectroscopy measurements.