A new method of resistless photochemical etching for silicon wafer is developed, which is using hydrogen peroxide (H 2O 2) and hydrogen fluoride (HF) as activated species, ArF ultraviolet laser as a photon source. Silicon wafer can be directly etched without photo-resists. When the concentration ratio of H 2O 2/HF is 1.3, the optimized etching was found. At the energy density of 29 mJ/cm 2 as well as the shot numbers of 10000, the maximum etching depth of 210 nm was obtained.