Abstract: Experimental results of proton irradiation effects are given for Floating gate ROMs. The proton irradiation effects in FLASH ROM and EEPROM are the total dose effects rather than the Single Event Effects. These are attributed to the accumulative dose of both original and secondary protons. There is a proton fluence threshold. Errors occur when proton fluence is above the threshold. It is easy to eliminate the damage produced by proton irradiation for 29C256 by annealing in power on under 100癈, however, it is difficult for 28C256. Data errors occur in devices that are measured during irradiation and irradiated in power on, moreover, new data cannot be written in these devices with programmer. However, under more proton fluence, there is no error in devices in power off mode and new data can be written in these devices with programmer. It is an effective method to backup some devices in power off mode to improve the reliability of spacecrafts in which FLASH ROMs and EEPROMs are used.