The Ge thickness, x, of NiAuGe(5 nm/45 nm Ix nm)/ZrB2(50 nm)/Au(20 nm) ohmic contacts to n-InGaAs was varied between 0 and 20 nm. The microstructures of these contacts, after annealing at 270-degrees-C, were investigated using transmission electron microscopy (TEM) and correlated with the respective specific contact resistances. In the absence of Ge, a Ni-Ga-As phase was formed at the metal-semiconductor interface and the specific contact resistance was high (0.63 OMEGA mm). When thicknesses of x = 1 0 nm or x = 15 nm of Ge were added, Ni-Ge-As phases were observed, but they were replaced by AuGeAs and NiGe when x = 20 nm. The specific contact resistance was a minimum (0.11 OMEGA mm) for this composition. Ge was clearly beneficial for ohmic-contact formation. The low-temperature I-V characteristics of the contact containing the largest amount of Ge (that is, x = 20 nm) indicated that electron tunnelling through degenerately-Ge-doped regions was not the dominant ohmic mechanism in these contacts.