We demonstrate a novel approach to improve the characteristics of the gold nanoparticle-based organic transistor memory devices by using self-assembled monolayers (SAM) with different functional groups as interfacial modifier. SAM-based interfacial engineering significantly improved the hysteresis, memory window, and on/off ratio of a nano floating gate memory (NFGM) at zero gate voltage. This NFGM showed a large memory window of up to 190 V and on/off current ratio of 105 during writing and erasing with an operation voltage of 100 V of gate bias in a short time, less than 1 s. Furthermore, the devices show excellent nonvolatile behavior for bistable switching. The ON and OFF state can be stably maintained for 103 s with an Ion/Ioff current ratio of 106 for a pentafluorophenyl trimethoxysilane modified device. The results suggested the importance of SAM-modified interface for the memory performance of NFGMs.