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We have investigated the morphology evolution of silicon surface by laser irradiation. A pulsed ns-laser interaction with silicon in aqueous medium can produce self-organized microporous concave cell array structure without any chemicals and auxiliary equipment. Low radiant power was applied to the photo-induced non-thermal silicon surface modification. At the early stage, hemispherical patterns of 2 ∼ 3 µm were formed, maintaining a constant distance from each other without merging. Due to the thermal properties of water, subsurface heating proceeds under the silicon surface. The molten surface leads to the surface modulation to form subsided areas or expansions by nucleation and coalescence, resulting in the formation of a concave cone-shaped porous surface with a diameter of 10 ∼ 20 µm. The AFM reveals that the hierarchical hemispherical structures of two different scales are progressing simultaneously from the early stage. Keywords: Porous surface, Self-organization, LIPSS