A selective pore-sealing of highly porous ultralow-k (pULK) dielectrics by a cyclic initiated CVD (iCVD) process has been successfully developed. A negligible increase of the pULK thickness and the k value was achieved even after the hermetic pore-sealing. The pore-sealed pULK films show low leakage current and excellent dielectric reliability, comparable to the commercialized low-k dielectric. The selective pore-sealing process does not deposit the pore-sealing layer on Cu surface. The porosity difference between pULK and Cu surfaces is attributed to the origin of the selectivity in the cyclic iCVD process.