SiGeSn is a new ternary alloy that allows for band gap tuning over a large energy range as well as band offset engineering with GeSn. Here the first vertical gate-all-around nanowire nFETs featuring a SiGeSn/GeSn/SiGeSn heterostructure are presented. The devices show a subthreshold swing (SS) of 71 mV/dec and a low off-current attributed to the expected larger bandgap and therefore suppressed gate induced drain leakage (GIDL). The results demonstrate that SiGeSn is an exciting alloy that extends the pure Ge and GeSn material properties.