The electrical behavior of organic memory devices based on pentacene thin film transistor using polymethylmethacrylate (PMMA) as the gate dielectric is reported. Memory behaviors based on incorporating a layer of thermally evaporated metallic floating gate are demonstrated. The gate electrode was made from 50 nm evaporated aluminum on glass substrate, and the drain and source electrodes were fabricated by evaporating 50 nm gold. The effects of the insulator thickness on the stability of pentacene layer are also investigated. The memory transistors containing the floating gate exhibited clear hysteresis in their electrical characteristics (output and transfer characteristics). Under an appropriate gate bias (2 s pulses), the floating gate is charged and discharged, resulting in significant threshold voltage shifts. Pulses of 1 V resulted in clear write and erase states. The shifts in the threshold voltage of the transfer characteristics were attributed to the charging and discharging of the floating gate. The detailed programming and erasing procedures are reported.