As the complementary metal-oxide semiconductor (CMOS) compatible with group IV materials, germanium tin (GeSn) alloys have potential applications in photonics and microelectronics. With the increase of tin (Sn) content, GeSn alloys can change from indirect bandgap semiconductor to direct bandgap semiconductor. On the other hand, GeSn alloys have a higher hole mobility than Ge and can be used as channel materials in metal-oxide-semiconductor-field-effect transistors (MOSFETs). Therefore, the properties of GeSn alloys are studied extensively. In this work, the solid-phase reaction between Ni and GeSn is investigated under microwave annealing (MWA) and rapid thermal annealing (RTA) conditions. We use the four-point probe method to measure the sheet resistance, the atomic force microscopy (AFM) to examine the surface morphology of the sample, the cross-section transmission electron microscopy (XTEM) to analyze the microstructures of the metal stanogermanides, and energy dispersive X-ray spectrometer (EDX) to observe the elements’ distribution of different samples. It is shown that the flat Nickel stanogermanide (NiGeSn) films are obtained at 300 ℃ for MWA and at 350 ℃ for RTA. By analyzing the distributions of sample elements, we find that Sn atoms continue to diffuse into the NiGeSn layer and are segregate mainly at the interface between NiGeSn and GeSn. However, the Ti atoms move from interlayer to the surface after being annealed. We propose that this method is a promising way of developing GeSn devices in the future.