High quality dielectric layers, e.g., high-k dielectric layers comprised of at least one refractory or lanthanum series transition metal oxide or silicate, for use as gate insulator layers in in-laid metal gate MOS transistors and CMOS devices, are formed by electrolessly plating a metal or metal-based dielectric precursor layer comprising at least one refractory or lanthanum series transition metal, such as of Zr and/or Hf, on a silicon-based semiconductor substrate and then reacting the precursor layer with oxygen or with oxygen and the Si-based semiconductor substrate to form the at least one metal oxide or silicate. The inventive methodology prevents, or at least substantially reduces, oxygen access to the substrate surface during at least the initial stage(s) of formation of the gate insulator layer, thereby minimizing deleterious formation of oxygen-induced surface states at the semiconductor substrate/gate insulator interface.

High quality dielectric layers, e.g., high-k dielectric layers comprised of at least one refractory or lanthanum series transition metal oxide or silicate, for use as gate insulator layers in in-laid metal gate MOS transistors and CMOS devices, are formed by electrolytically plating a metal or metal-based dielectric precursor layer comprising at least one refractory or lanthanum series transition metal, on a semiconductor substrate, typically a silicon-based substrate, and then reacting the precursor layer with oxygen or with oxygen and the semiconductor substrate to form the at least one refractory or lanthanum series transition metal oxide or silicate. The inventive methodology prevents, or at least substantially reduces, oxygen access to the substrate surface during at least the initial stage(s) of formation of the gate insulator layer, thereby minimizing deleterious formation of oxygen-induced surface states at the semiconductor substrate/gate insulator interface.