The design and characterization of the InSe/BN heterojunction were investigated by study of optical reflectance, transmittance, and absorbance spectra in the incident wavelength range 300–1100 nm. Three absorption band edges related to conduction–valence band splitting of 2.75, 1.49, and 3.90 eV were observed. These bands shifted to 1.06 eV, 2.25 eV, and 3.85 eV on preparation of the InSe/BN interface. Analysis of dielectric spectra in the frequency range 275–1000 THz revealed the presence of three main resonance peaks at 333, 308, and 280 THz for the InSe substrate and at 341, 316, and 286 THz for the InSe/BN interface. The dispersion energy of the substrate increased from 27.43 eV to 33.77 eV on preparation of the InSe/BN interface. The quality factor of the heterojunction was found to be three times greater than that of InSe. The device seems to have potential, because the results suggest use of the heterojunction in thin-film transistor and optical communication technology.