The flash memory has been evolved from floating gate to the nitride-trapping storage type-SONOS, and even progresses toward the nano-crystal memory in the future. Among them, floating gate flash memory has been one of the most successful nonvolatile memories for the largest volume production, in the past two decades. In comparison, SONOS-type trapping storage has reliability issue and has yet not been fully approved for mass production. On the other hand, the floating gate flash memory requires high control gate voltage for programming which limits the device scaling and reliability, while the SONOS type flash needs to overcome the reliability issues, especially the tunnel oxide and data retention. In this paper, we address different strategies for designing SONOS-type flash memories with low voltage operation, for achieving good reliability while keeping high speed performance. Various schemes will be demonstrated to meet the low voltage and high speed requirements. Also, the strategies for achieving excellent data retention will be specifically presented.