We studied the effect of post-anodization chemical etching on porous silicon by means of photoluminescence (PL), Fourier transform infrared (FTIR) absorption and Raman spectroscopy. We performed these measurements with repeating etching and then observed the variation of the spectra. On the basis of the correlation between PL and FTIR spectral changes, the PL emission at 660 and 730 nm in PL spectra stems from Si-H2, and Si-H clusters at surface, respectively. Raman spectra show a close relation between PL emission at 850 nm and nanocrystallites in porous silicon. In addition, chemical etching contributes to the promotion of nanocrystallites and to dissolving them.