The advances in the growth of pseudomorphic silicon-germanium epitaxial layer combined with the strong need for high-speed CMOS VLSI circuit have led to increased interest in silicon-based heterojunction MOSFET's transistors. The high-performance heterostructure SiGe MOSFET exhibits higher channel mobility than its bulk Si counterpart. The most critical and challenging process for fabricating a SiGe MOSFET device is that for making a gate oxide with sufficient quality for useful conductivity modulation. PECVD methods was employed to deposit the gate oxide and C-V method was used to investigate the electrical characteristics of the film. For PECVD gate oxide, a film refractive index 1.47 were obtained using the deposition rate 125Å/min with a break down voltage 4-5 MV/cm, which deposition conditions are optimized as flow rate of DES (12sccm), N20(172sccm), Helium(850sccm), temperature 300°C, power density 0.09W/cm². The total interface trap and fixed charge density N_t=5.4x10¹² cm^-2 and flatband voltage V_fb=-16V for non-armealing MOS capacitor and the total effect of interface trap and fixed charge density 6.4x10¹¹ cm^-2 and flatband voltage 4V were obtained at the oxide thickness d_ox=1160Å using annealing at 650°C for 30 minutes in the ambient of nitrogen. LPCVD silicon dioxide film was obtained at the deposition rate 14.5 Å/min and refractive index 1.46 while N_t=3.9x10¹²cm^-2 and V_fb=-8V for nonannealing and N_t=4.9x10¹¹ cm^-2 and V_fb=-2V for 650°C annealed MOS capacitor.