Abstract: A method for determining the impurity concentration of impurity-doped polysilicon layers in semiconductor wafers is provided. Through experiments, it is found that the reflectivity of an impurity-doped polysilicon layer is nearly a regular function of the impurity concentration thereof. Accordingly, an impurity-doped polysilicon layer having an unknown impurity concentration can be determined by first measuring the reflectivity thereof by illuminating the impurity-doped polysilicon layer with light, and then using mapping transformation to find the corresponding value of impurity concentration of the impurity-doped polysilicon layer. This method can be used instead of the conventional thermal wave method that often result in having to discard the wafers due to the incapability of reliably determining the impurity concentration of the polysilicon layers formed on the semiconductor wafers.