Monolayer passivation of the silicon(001) surface by selenium is investigated in an ultrahigh vacuum environment with a solid selenium source by reflection high-energy electron diffraction and residual gas analysis. It is found that precisely one monolayer of selenium is deposited on silicon(001) when the silicon substrate temperature is set slightly above the selenium source temperature and the passivation time ensures a little overdose of selenium above one monolayer. The temperature settings prevent selenium condensation on silicon(001), which makes selenium deposition on silicon(001) a thermodynamically self-limited process to exactly one monolayer. (c) 2006 Elsevier B.V. All rights reserved.