We investigate by photoacoustic spectroscopy the optical band‐gap energy of mercuric iodide, &agr;‐HgI2, grown by sublimation in a sealed ampoule. Due to its importance as a detector material operating at ambient temperature, the physical properties of &agr;‐HgI2have been recently studied. We found, by two different methods, the band‐gap energiesEG=2.32 and 2.39 eV, respectively. These results are in good agreement with recent measurements based on reflection and absorption spectra. ©1995 American Institute of Physics.