In this work, the components of fin top and fin sidewalls of tri-gate fin field-effect transistor (FinFET) were distinguished and extracted by a proposed method to find out the characteristic and reliability. Poor fresh characteristic could be found on fin sidewall area due to the existed surface defects after the fabrication the Si etching process. After NBTI stress, larger VTH shift and severe SS degradation reveals worse reliability on fin top area. The result indicates that the poor initial characteristics of the fin sidewalls will reduce the performance of tri-gate FinFETs, but the poor reliability of the fin top determines the overall degradation of the device.