The Si(Ge) alloy is currently used in the Complementary Metal Oxide Semiconductor (CMOS) technology, improving device performances, decreasing power consumption, and allowing stress engineering in Sibased devices. If Si(Ge) is used in transistors' source, drain and gate, it is necessary to create ohmic contacts between the first-level metal and Si(Ge). In the current Si-based CMOS technology, ohmic contacts are created via the reaction of a thin Ni(Pt) layer with doped-Si, aiming to form a thin NiSi layer on the Si substrate. A similar process should be used on Si(Ge). In this work, the first stages of Ni reaction with Si(Ge) is investigated using high resolution transmission electron microscopy and laser-assisted atom probe tomography. The first stage of Ni/Si(Ge) reaction leads to the formation of a germanosilicide layer made of Nip(Si1-xGex)(q) nano-grains exhibiting different structures and compositions. The formation of Nip(Si1-xGex)(q) phases occurs at temperatures as low as 60 degrees C. The germano-silicide grains exhibit coherent interfaces with the Si(Ge) layer, and during their growth, a fraction of the Ge atoms initially located in Si(Ge) is pushed from the Nip(Si1-xGex)(q)/Si(Ge) interface into the Si(Ge) layer, leading to Ge accumulation at this interface. This phenomenon can cause Ge accumulation up to 100%, promoting the incorporation of Ge-pure nanometric inclusions inside the germano-silicide layer. (C) 2016 Elsevier B. V. All rights reserved.