Abstract: Process for thin-film electroless-plated deposition onto the substrate, which is either hydrophilic or hydrophobic silicon based dielectric material (e.g., silicon dioxide, silicate glass, or polysiloxanes), is a substitute for the conventional sensitization/activation route by pre-treating the surface of the dielectric substrate by plasma (H2/N2, N2, H2, or O2), immersing the substrate in a basic aqueous solution for removing hydrogen, immersing the substrate in a basic aqueous solution of metal ions for adsorbing the metal ions thereon, reducing the metal ions on the surface of the substrate, and immersing the substrate in an electroless-plating solution to deposit an electroless-plated metal film. The substrate formed of hydrophobic polysiloxanes which is properly pretreated by gaseous plasma can be immersed in a basic solution with strong oxidizing capability and/or performing a selective pattern by plasma treatment.