Electron cyclotron resonance (ECR) plasma thermal oxide has been investigated as a gate insulator for low temperature (less-than-or-equal-to 600-degrees-C) polysilicon thin-film transistors based on solid phase crystallization (SPC) method. The ECR plasma thermal oxide films grown on polysilicon film has relatively smooth interface with polysilicon film when compared with the conventional thermal oxide and it shows good electrical characteristics. The fabricated poly-Si TFT's without plasma hydrogenation exhibit a field-effect mobilities of 80 (60) cm2 /V . s for n-channel and 69 (48) cm2/V . s for p-channel respectively when using Si2H6 (SiH4) source gas for the deposition of active poly-Si film.