Experimental results of irradiation effects are given for Floating gate ROMs. The proton and neutron irradiation effects in FLASH ROM and EEPROM are total-dose effects rather than single event effects. This is confirmed by γ irradiation. There is a fluence dose threshold. Errors occur when the fluence dose is above the threshold, whereas no error occurs below this threshold. Data errors occur in devices that are in measuring during irradiation or irradiated in power on mode, thus new data cannot be written in these devices with programmer. However, under more fluence dose, there can be no error in devices in power off mode, and new data can be written in these deviceswith programmer. At the beginning of the occurrence of errors, the address and value of the error are at random.