We have investigated the effects of deep hydrogen implantation into n- and p-type silicon wafers ((100) oriented, with resistivity in the 1-20 Ω·cm range). Deep implantation has been achieved using the Hitachi-AccSys PL-7 RF LINAC set for 3.0 MeV beam energy, degraded to 1.8 MeV. Hydrogen has been implanted 30 μm below the wafer surface with an implant dose (fluence) >5×1015 cm-2. Samples were partly covered by a metal mask during implant. Porous silicon has been formed on the exposed samples to study the effect of hydrogen irradiation. We have found that porous silicon formation is inhibited in the irradiated areas on p-type silicon and promoted on the n-type one. Copyright © 2015 CC-BY-3.0 and by the respective authors.