The electron-trapping characteristics of W in SiO2 have been studied using evaporated and ion-implanted W. The evaporated W results indicate a trapping cross section varying from 1.56×10-14 to 4.62×10-14 cm2 depending on the evaporation time. The cross section of the implanted W is 1.06×10-15 cm 2. Thermal-detrapping measurements indicate an activation energy of 0.9 eV, whereas optical detrapping is not observed for light energies up to 6 eV. It is not understood why there is this large discrepancy of results. It is also interesting to note that Powell and Beairsto measured a barrier height of 3.6 eV for the W-SiO2 interface.