We have fabricated resonant tunneling structures having a buried ErAs semimetallic quantum well and AlAs double barriers, on (001)GaAs substrates. In order to suppress the three‐dimensional island growth of GaAs and AlAs on ErAs and to obtain flat interfaces, we adopted a template approach, in which one monolayer of Mn was deposited on ErAs prior to the growth of AlAs, in molecular beam epitaxy. In the current–voltage characteristics at room temperature, negative differential resistance was clearly observed in a significant number of diodes with the ErAs thickness ranging from 2.6 to 5.0 nm. This room‐temperature device operation on (001) substrates is, we believe, an important step towards the realization of semimetal/semiconductor hybrid quantum devices. © 1996 American Institute of Physics.