In this study, we investigate the effects of amorphous silicon (a-Si) mass density variations on the electrical series and contact resistance of nanoscale structures for thin-film transistors (TFTs). Impurity distributions according to the variation of a-Si mass density (ρ a-Si) are obtained from Monte-Carlo (MC) method and the resistance extraction are performed by using device simulation based on transfer length method (TLM) with a-Si mobility and Schottky contact model. Under the small variations of ±5% from standard ρ a-Si, electrical resistances are significantly changed with 30% variations from its typical characteristics in nanoscale TFTs.