In this work, the masking technology for selective porous silicon formation by creating n-type areas on a p-type substrate by ion implantation was investigated and the optimum conditions were found. The most critical parameter in the process is the surface concentration of dopants. However, in all cases, some corrosion of the masking area was observed. The main efficiency-limiting factor of the technique is pointed out and a solution is proposed. The optimum conditions developed were used to fabricate suspended monocrystalline silicon membranes on bulk silicon.