Macroporous silicon was fabricated on selected areas on p+ silicon substrate by anodization in HF x Ethanol solution. Pore size was ~ 130 nm. By high temperature thermal oxida-tion, a thin SiO2 layer was formed on pore walls. MOS ca-pacitors with Al metallization were then fabricated and the samples were characterized by dielectric spectroscopy (DS) in the frequency range 1 Hz–1 MHz and in the temperature range 173–353 K. The results reveal that at low temperatures the dielectric constant ε΄ is independent of frequency (tox = 20 nm ε΄~3.4, tox = 40 nm ε΄ ~ 2.8, tox = 72 nm ε΄ ~ 2.6). A theo-retical model, based on Vegard’s law, which calculates the static dielectric constant of the samples, was used. The calcu-lated theoretical values are in good agreement with the experimental results. Dielectric loss data show that the oxidized samples exhibit values of tanδ < 10–2 which are smaller than those of the non oxidized samples. The obtained dielectric characteristics enable oxidized macroporous silicon thick layers to be good candidates for use in RF isolation on a silicon substrate. Transient current measurements were also performed at room temperature for voltages from 1.0 to 20.0 V in the time interval 1-100s in accumulation. The analysis of the experimental data reveals that the conductivity is gov-erned by two different conduction mechanisms. In the low applied voltage region the conduction is due to thermally ex-cited electrons, hopping from one state to another. For higher voltages Fowler-Nordheim (F-N) tunnelling of electrons through the oxide prevails.