Among the technologies for integrating GaAs devices with Si VLSI chips, epitaxial liftoff (ELO) is conspicuous for maintaining the quality of the single crystal epitaxial GaAs films. Traditionally, ELO is implemented in aqueous HF solution. It would be cleaner and simpler if ELO could be implemented in a vapor process. In this article, we will present the potential improvements in the ELO process by using a vapor phase etch to undercut thin films.