Degradation of the tunneling oxide film in EEPROM and FLASH memory test structures has been studied. Two models have been used to characterize the tunneling induced degradation of the oxide thin film. They are the effective tunneling area model and the effective oxide field model. These two models correspond to the two extreme cases of oxide charge trapping. Our study not only suggested an accelerated reliability test method for the tunneling oxide film, but also provided a description of the oxide charge trapping process during Fowler-Nordheim tunneling. The generation mechanism of the oxide trapped charge is discussed.