Polysilicon thin films with nanometer-sized patterns were etched in a high density inductively coupled plasma (ICP). The etch characteristics of polysilicon and silicon oxide thin films were examined using HBr/Ar gas chemistry. As the concentration of HBr gas increases, the etch rate of polysilicon film and the etch selectivity of polysilicon to photoresist simultaneously increase. The etch profiles of polysilicon films masked with photoresists were observed for various nanometer-sized patterns of 50 ~ 125 nm lines. In this study, the good pattern transfer of polysilicon films with nanometer-sized patterns was achieved using HBr/Ar etch gas.