We have investigated the effects of UV irradiation on the electrical and optical properties of polycrystalline In2 O3 films. We found that UV illumination at a peak wavelength of 365 nm leads to a sharp drop in resistance and increase in carrier concentration. This highly conductive state persists for a timescale of hours in air at room temperature after illumination. We observe distinct changes in the optical absorption spectra and the associated change in carrier concentration, which is consistent with a Burstein-Moss shift of ∼0.1 eV. The relaxation rate of this persistent conducting state depends strongly on temperature. We find that the conductance relaxation in an oxygen-free environment can be described by a stretched exponential while the behavior of the samples in air is better described by a logarithmic relaxation, both of which may be associated with glassy behavior. © 2009 American Institute of Physics.