We report here the first study of formation kinetics of vertically-aligned periodic Si nanorod arrays on (001)Si substrates in H2O2/HF/EtOH etching solutions. The diameter, length, location, and crystallographic orientation of the Si nanorods produced were well-controlled using the colloidal nanosphere lithography combined with the Au-assisted selective chemical etching process. The as-synthesized Si nanorods were determined to be single crystals and the axial orientation of the Si nanorods was identified to be parallel to the  direction, which was identical to the orientation of the (001)Si wafers used. The lengths of Si nanorods could be tuned from sub-micrometer to several micrometers by adjusting the etching temperatures and time. The activation energy for the formation of Si nanorods array on blank-(001)Si was about 76.7 kJ/mole, which was calculated according to the Arrhenius plot. From water contact angle measurements, it is found that the Si substrate with Si nanorod arrays exhibited a more hydrophobic behavior compared to the blank-(001)Si sample. The hydrophobic behavior of the HF-treated Si nanorod arrays could be explained by the Cassie-Baxter model.