Time-of-Flight (TOF) measurements have been performed on n-type TiO2/p-type CuInS2 heterojunctions. The TiO2 film thickness has been varied between 200 and 400 nm, while the CuInS2 film thickness has been fixed at 500 nm. The TOF response can be accurately modeled, if the potential drop across the p-n heterojunction with a large density of interface states is properly accounted for. Also electron transport in a space-charge region for a not fully depleted semiconductor has to be considered. The electron mobility in TiO2 is found to be 10?2?cm2?V?1?s?1, independent of the TiO2 layer thickness. The interface-state densities are 5×1011, 2×1012, and 6×1012?eV?1?cm?2 for 200, 300, and 400 nm thick TiO2 films, respectively.