Ga and Sn surface-segregated GeSn (Seg. p+-GeSn) layer with an average active Ga doping concentration of $3.4 \times 10^{20}$ cm $^{-3}$ and surface Sn composition of ~7% was grown on the Ge (100) substrate by molecular beam epitaxy. An ultralow specific contact resistivity $\rho _{\textsf{c}}$ down to $4.4 \times 10^{-\textsf {10}} \,\,\Omega \cdot \text {cm}^{\textsf {2}}$ is achieved for the Ti contact on Seg. p+-GeSn film. Average $\rho _{\textsf{c}}$ , extracted from 14 sets of nano-scale transmission line method test structures and a collection of more than 90 devices, is $6.5 \times 10^{-\textsf {10}} \,\,\Omega \cdot \textsf {cm}^{\textsf {2}}$ . This is the lowest $\rho _{\textsf {c}}$ for any nonlaser-annealed contacts. In addition, the benefits of Ga and Sn surface segregation on $\rho _{\textsf {c}}$ reduction were investigated. Increasing the surface Sn composition from 5% to 8% lowers $\rho _{\textsf {c}}$ from $1.4\times 10^{-\textsf {9}}$ to $1.1\times 10^{-\textsf {9}} \,\,\Omega \cdot \textsf {cm}^{\textsf {2}}$ and the Ga surface segregation further reduces $\rho _{c}$ down to $6.5\times 10^{-\textsf {10}} \,\,\Omega \cdot \textsf {cm}^{\textsf {2}}$ .