Small sized surface acoustic wave (SAW) duplexer for wide band code division multiple access (W-CDMA) system with a good temperature coefficient of frequency (TCF) and good frequency characteristics has been required. However, the size of conventional SAW duplexer for W-CDMA using Al-electrode/50- 70°YX-LiNbO3 is large (3.8 × 3.8mm2) and its TCF is not good (-80ppm/°C). So, this duplexer can't satisfy its severe specifications in the all temperature range from -30 to 85°C. When SiO 2 film is deposited on this substrate to improve the TCF, the frequency characteristics is deteriorated by convex portions on the SiO 2 surface caused by SiO2 sputtering. This time, by applying a flip chip bonding process, a flattened-SiO2/Cu-electrode/ substrate structure, and a YX-LiNbO3 substrate, a small sized (3×2.5×1.2mm3) SAW duplexer having good characteristics (such as low insertion loss and large attenuation) and good TCF has been realized for the first time. Here, the SiO2 film is used to improve the TCF, the flattened-SiO2 to obtain high Q, the thick Cu-electrode to obtain the large reflection coefficient, and the YX-LiNbO3 substrate to obtain the large coupling factor and not to generate Rayleigh wave which causes spurious at the SiO2 of 0.3λ and the Cu-electrode of 0.05λ.