Based on measurements of the spectrum emitted by a target, a new method for measuring temperature, the peak-wavelength method (PWM), is proposed and evaluated in this paper. The uncertainty and resolution of this method have been estimated theoretically, and it is shown that this method offers high resolution and accuracy. Moreover, several analyses have been done for various surfaces (non-blackbody) with a series of assumed spectral emissivities. The results show that better accuracy can also be obtained in these cases. Finally, an experimental setup using a Fourier transform infrared spectrometer was built and tested in our lab. Several experiments have been carried out that show the peak-wavelength method is feasible and practical.