A nonvolatile memory effect was observed in an organic thin-film transistor by introducing a Boating gate structure. The Boating gate was composed of an Al film in a thickness of nanometers, which was thermally deposited on a SiO2 insulator and exposed to air to spontaneously oxidize. It can be seen that the transistors exhibit significant hysteresis behaviors and storage circles in current-voltage characteristics in the dark and under illumination, indicating that the transistors may act as a nonvolatile memory element. The operational mechanism is discussed in the cases of dark and illumination via charge trapping by the Al floating gate.