Two simple and easy processes have bean demonstrated to fabricate two-dimensional (2-D) nanostructure array on Si surfaces by using only focused beam patterning and wet etching. First, we took advantage of the enhanced etch rate (ER) of electron-beam-exposed SiO2 in HF based solution. A 30-nm thick oxide layer was shot with 30-keV focused-electron beam with spot doses ranging from 20 to 140 pC/dot. After development of SiO2 layer in 1% HF solution, the Si substrate was etched by hydrazine (N2H4H2O) to form pyramidal etch-pits. By using this process, 50-nm concave nanopyramid array (NPA) with 100-nm period can be fabricated successfully. Second, we utilized the newly found retarded ER of ion-beam-exposed Si in hydrazine. 2-D arrays of dots were written directly on the Si substrate with 60-keV Si focused-ion beam (FIB) with a dose of 5 x 10(14) ions/cm(2). The Si substrate was then dipped in hydrazine solution, where the unexposed region was selectively etched by hydrazine. By using this process, 100-nm convex NPA with 200-nm period can be fabricated easily. The performance of the proposed processes is compared in terms of pattern size, throughput and process diversity.