This work focuses on the nanopatterning of sub-10 nm InGaAs fins by inductively coupled plasma reactive ion etching for advanced III−V n-fin field effect transistors (n-FinFETs) on silicon. First, different chlorine chemistries have been investigated and compared in order to select the most adequate one for the FinFETs process. Following this analysis, the BCl3/SiCl4/Ar mixture was selected for the remaining of the work. Thus, a systematic study of the etching process based on this chemistry has been carried out, and the effects of the experimental conditions on the etching kinetics and the sidewalls quality have been revealed. The optimized results depict 8 nm width fins with smooth (line edge roughness ≈2 nm) and almost vertical (85° ± 1) sidewalls, opening the way for sub-10 nm width InGaAs FinFETs on silicon.