Formation of CuInS2 by modifying the In2S3 surface was attempted by solution incorporation reaction. An In2S3/In2O3 pellet was dipped in a solution containing copper( I) chloride and hydroxyl ammonium chloride at 95 degrees C for 10 s. The X-ray diffraction pattern and diffuse reflectance spectra changed by the chemical treatment indicated formation of a CuInS2 thin film on the surface of In2S3. The dark and photocurrent voltage curves measured in the poly-sulfide solution demonstrated the thin film on the surface of In2S3 is a p-type semiconductor. By annealing at 400 degrees C, the semiconductor type was changed from p to n.