We have measured Fourier transform infrared (FTIR) spectra ofCr3+immersed porous silicon after annealing at different temperatures. After dipping porous silicon intoCr3+solution, three additional peaks appear at 807, 886, and940 cm−1in the FTIR spectrum. When annealed in nitrogen at different temperatures for various durations, the peak at807 cm−1remains almost unchanged, the height of peak886 cm−1decreases gradually, while the peak at940 cm−1disappears quickly. This decay process occurs much faster at higher annealing temperature. These FTIR features reflect the surface chemistry change after immersed intoCr3+solution.