The performance of Pd–Ge based ohmic contacts, with and without Ti–Pt or Ti–Pt–Au capping layers, has been investigated. The contacts were deposited by electron beam evaporation, then characterized electrically using a modified transmission line method (TLM) and structurally using both cross-section and plan-view transmission electron microscopy (TEM). Although both capped and non-capped contact structures underwent the same phase transformations during annealing, capped contacts had significantly better contact resistances (a minimum value of 4×10-7 Ω cm2 was achieved) – almost three orders of magnitude better. The superior performance is attributed to the capping layers providing protection for the Pd–Ge layers during contact processing, where the metallization was exposed to a CF4–O2 plasma, oxyen descumming, organic solvents and deionized water. Non-capped contacts exhibited PdGe decomposition and oxidation of exposed Ge. Long-term reliability testing of capped contacts showed virtually no change in contact resistance at 235°C (1350 h) and a sevenfold increase after ageing at 290°C for 370 h. There were no phase changes during ageing; the increase in contact resistance was attributed to interdiffusion between Ge and GaAs.