Hf-Ni alloys are studied as a gate electrode for metal-oxide-semiconductor devices. The Hf-Ni solid-state amorphization couple encompasses several metallurgical phenomena which are investigated at the nanoscale and are correlated with the macroscopic electrical properties of devices. The dependence of the Fermi level position on the alloy composition is studied both on SiO 2 and on HfO 2. In order to isolate the effects of interfacial and dielectric charges and dipoles, the dependence of the vacuum work-function values on the composition is also studied. The Fermi level positions of the alloys do not depend linearly on the average composition of the alloys and are strongly affected by Hf enrichment at the HfNi x/dielectric interface and the HfNi x surface. We note a constant shift of 0.4 eV in the Fermi level position on HfO 2 compared to SiO 2. In addition, characterization of the composition, structure, and morphology reveals Kirkendall voids formation when the bottom layer consists of Ni, and an oxygen-scavenging effect when the bottom layer is Hf.