Transient photocurrents associated with optical depopulation of electron trapping centers have been studied as a function of photon energy in thin amorphous silical films grown on silicon wafers. A summary is given of the application of this technique to determine inhomogeneous trap state distributions in silica films. Electron trapping distributions observed at 1.9 eV and 2.5 eV below the conduction band edge of the silica and having densities of 1014/cm3are reported. Measurements at liquid‐nitrogen temperature indicate the presence of shallow trapping states of similar concentration levels in addition to the deep trap distributions.