Resistive switching of metal-insulator-metal (MIM), consisting of a metal-organic chemical vapour deposition (MOCVD) TiO₂ layer sandwiched between Pt electrodes, has been measured systematically before and after thermal annealing in different ambiences. With H₂ annealing at 400°C, the current level in the high-resistive state (HRS) significantly decreased while little change in the low-resistive state (LRS) was observed. As a result, the switching ratio over 7 orders of magnitude at the current level was obtained. From the analysis of current-voltage (I-V) characteristics in HRS and LRS, we found that the LRS was characterized with an ohmic conduction, while in the HRS after H₂ annealing, charge trapping became significant as a result of a significant decrease in the current level. In a separate experiment, a partial reduction in TiO₂ was detected using high-resolution X-ray photoelectron spectroscopy (XPS) after resistant-state switching from HRS to LRS by using a Hg probe as a top electrode, which is associated with filament formation.