We demonstrate the characteristics of p+-Ge/n-Si and n +-Ge/p-Si heterojunction diodes formed by heteroepitaxial Ge grown on Si leading to high performance and very low leakage current. The ON/OFF current ratio of the p+-Ge/n-Si and n+-Ge/p-Si heterojunction was >107 and >106, respectively. The OFF current density was extremely low at <10μA cm2 for the p +-Ge/n-Si formed with different implantation energies of 10∼40 KeV and ∼ 20μ A cm2 for the n+-Ge/p-Si with different implantation energies of 20-50 KeV at a reverse bias of $\vert V R=±1 V, respectively. Both p and n-Ge channel multifin field-effect transistors (FinFETs) were formed by a mesa structure using these p +-Ge/n-Si and n+-Ge/p-Si heterojunctions. A high-κ/metal gate stack was employed. The body-tied Ge multifin FinFET with a fin width (W Fin) of ∼ 40 nm, and the channel length (LChannel) was 150 nm for p-FinFET and of 110 nm for n-FinFET, exhibiting a driving current of 174 μ A/μ m at V G=2 V and 102 μ Aμ m at V G=2 V , respectively. This is the first experimental demonstration of a body-tied high mobility Ge channel multifin FinFET using a top-down approach.