Arsenic has a tendency to evaporate during high temperature annealing of GaAs. This process can have deleterious consequences for electrical properties of the contact to GaAs and must be controlled during annealing by encapsulants. It would also be advantageous if this cap could be integrated in the contact metallization scheme for GaAs. In this work we compare the behavior of conducting thin-film encapsulants of mere GaAs and of GaAs covered with a Pd film upon furnace annealing. Thin films of Pd are used on GaAs to form a contacting layer by reaction with GaAs. This reaction complicates the encapsulation task because it causes stresses in an already strained thin film encapsulant. We report on experimental study of conducting encapsulants mainly; W, Hf, HfN, and TaSiN, but others have been tried, too. They were sputter-deposited on top of GaAs and GaAsPd samples. During annealing in argon we monitored the evaporants with a thin Cr film deposited on silicon nitride and resting face to face on the encapsulated sample. The captor layer was then analysed by backscattering spectrometry. We found out that Pd enhances As evaporation and GaAsPd could not be encapsulated. The reasons for this will be discussed.