The pass-bands of a transmission (Tx) and a receiving (Rx) of the Personal Communication Services, (PCS) handy phone in US are 1850-1910 MHz and 1930-1990 MHz, respectively. The transition bandwidth between the Tx and the Rx is very narrow as 20 MHz compared with other systems. A duplexer for the PCS using surface acoustic wave (SAW) requires a SAW substrate, which has a the good temperature stability, an optimum electromechanical coupling factor, and a large reflection coefficient. Some of Rayleigh waves and leaky SAWs (LSAWs) on various substrate or structures have a good temperature characteristic, but almost all of them have not a optimum coupling factor and a large reflection coefficient for the US-PCS duplexer. In 2003, authors reported the US-PCS SAW duplexer having good temperature stability, a steep frequency characteristic in transition band, a low loss, and a large out-of band suppression . This paper describes the detail of the new substrate having the good temperature stability, the optimum electromechanical coupling factor, and the sufficient reflection coefficient.