order to continue scaling electronic devices, an alternative gate material with high dielectric constant (high-k) has been proposed for capacitors, memories, and optoelectronic devices in future complementary metal-oxide-semiconductor (CMOS) generations. At present, HfSiON has gained much attention to be one of the most promising candidate materials to replace conventional SiON-based dielectrics. This chapter is focused on the synthesis and properties of HfSiON prepared by radio frequency magnetron reactive sputtering (RFMRS). This chapter is organized as follows. The scaling issue and major requirements of high-k gate dielectrics are described in Section 1. The fabrication process and properties of HfSiON films deposited by RFRCS are discussed in detail in Section 2. Conclusions and potential future developments are presented in Section 3.