A new simple nondestructive method for band‐gap estimation in HgCdTe layers is presented in this work. The theoretical approach is based on a qualitative empirical model that assumes two different regions of absorption in HgCdTe. The border between the two regions, which indicates the approximate value of the band gap, is determined by differentiation of the absorption coefficient in respect to the photon energy. The approach is verified by experimental measurements on several HgCdTe layers grown by different techniques. First, the transmission is measured by Fourier transform infrared (FTIR) spectroscopy at room temperature; then, the measured data is smoothed and the absorption coefficient extracted. The absorption coefficient is then differentiated twice in respect to the photon energy which allows estimation of the average band gap and band‐gap variations within the HgCdTe layer. It appears that this simple procedure can assist in monitoring the quality of HgCdTe layers and help predicting the cutoff wavelength of HgCdTe photodiodes. ©1995 American Institute of Physics.