Various forms of wafer bonding have now emerged as a serious competitor to heteroepitaxy for optoelectronic integration of dissimilar semiconductor materials. Among the types of wafer bonding, perhaps the most flexible is that which employs free‐standing III–V films as created by epitaxial liftoff. For some purposes, weak Van der Waals forces provide an adequate bond between the native oxides of the III–V film and its new substrate. If the substrate is coated by palladium however, a low temperature solid‐phase‐topotaxial reaction occurs, producing oriented Pd4GaAs under the GaAs film. In effect, the topotaxy comes about through mechanical contact alone. The resulting metallurgical bond is an ohmic contact, a thermal contact and a robust, permanent, adherent contact.