High quality HfSiON/SiO2 gate dielectrics were successfully formed using a hot wall batch system, which is suitable for mass production. The carbon contamination at HfSiON/SiO2 interface was reduced by a sequential process of the interfacial layer (IL) formation and HfSiOx metal organic chemical vapor deposition (MOCVD). The O3 treatment was found effective to reduce the residual carbon and hydrogen, while the NH3 treatment made the HfSiOx to be HfSiON, which was effective to prevent the phase separation and crystallization during the activation annealing. The NH3 treatment temperature above 700°C is necessary to suppress the boron penetration during the activation annealing at 1050°C for 1 sec in p-channel field effect transistor (p-FET). Equivalent oxide thickness (EOT) of 1.37 nm was achieved for HfSiON· (3nm)/SiO2(0.5nm) gate stack using poly-Si electrode. High effective mobility of 271/62 cm2/Vs (n/p at 0.8 MV/cm) was obtained.