A simple process to fabricate two-dimensional (2-D) concave nanopyramid array (NPA) with nanometer period on Si surface has been developed by using electron beam (EB) irradiation and wet etching. The enhanced etch rate (ER) of EB-exposed SiO2 in HF-based solution has been utilized. Mask oxide layers with the thicknesses of 11-30 nm were shot with 30-keV focused EB at spot doses ranging from 20 to 140 pC/dot. EB-exposed SiO2 layers were selectively etched by dipping in 1% HF or buffered HF (BHF). The Si substrates were then dipped in anisotropic etchant hydrazine (N2H4 . H2O) to form concave NPAs. where patterned SiO2 layers were used as etch mask. By using this simple process, 50-nm period concave NPA with the size of 20 nm was fabricated successfully.