The present invention provides a method of fabricating a thermally stable polysilicon/high-k dielectric film stack utilizing a deposition method wherein Si-containing precursor gas which includes silicon and hydrogen is diluted with an inert gas such as He so as to significantly reduce the hydrogen content in the resultant polysilicon film. Semiconductor structures such as field effect transistors (FETs) and capacitors which include at least the thermally stable polysilicon/high-k dielectric film stack are also provided herein.