We report the observation of a field‐emission effect in SiO2/Si samples assisted by the presence of photons. Electric fields in the oxide of the order of 10 MV/cm−1are attained by photocharging during x‐ray illumination and bring the vacuum level to a position below the equilibrium Fermi level. Hot electrons are injected from the Si substrate, traverse the SiO2layer, and are emitted directly into vacuum. The large photocharging effect is related to the surface topography, consisting of multiple Si tips of about 1 &mgr;m high. ©1996 American Institute of Physics.