A comprehensive study of morphology of Reaction-Induced Vapor Phase Stain Etched porous silicon was performed in order to inspect samples for fractal structure and to estimate their potential for sensing applications. A new dual fractal structure is found in porous silicon layer obtained by Reaction-Induced Vapor Phase Stain Etch. The layer consists of two superposed fractal macro-and nanostructures. The macrostructure is formed due to the condensation of drops while the nanostructure is caused by the chemical reactions of the vapor molecules with the silicon surface. A comparison with morphology of porous silicon prepared by Liquid Phase Stain Etch is also presented.