A plating bath for electroless deposition of gold and gold alloy layers on such silicon-based substrates, includes Na(AuCl4) and/or other gold (III) chloride salts as a gold ion source. The bath is formed as a binary bath solution formed from mixing first and second bath components. The first bath component includes gold salts in concentrations up to 40 g/L, boric acid, in amounts of up to 30 g/L, and a metal hydroxide in amounts up to 20 g/L. The second bath component includes an acid salt, in amounts up to 25 g/L, sodium thiosulfate in amounts up to 30 g/L, and suitable acid, such as boric acid in amounts up to 20 g/L.