In order to address the metal oxidation issue in cermet solar thermal absorbers at high working temperatures, we developed solution-processed plasmonic Ni nanochain-SiO<sub>x</sub> (x≤2) selective solar thermal absorbers that exhibit high solar absorption, low thermal emittance, and strong anti-oxidation behavior up to 600 °C in air. The thermal stability is far superior to more conventional Ni nanoparticle-Al<sub>2</sub>O<sub>3</sub> selective solar thermal absorbers, which readily oxidize at 450 °C. Ni nanochains were embedded in SiO<sub>x</sub> and SiO<sub>2</sub> matrices which are derived from hydrogen silsesquioxane (HSQ) and tetraethyl orthosilicate (TEOS) precursors, respectively. Fourier transform infrared spectroscopy (FTIR) shows that the dissociation of Si-O cage-like structures into Si-O networks helped to retard the oxidation process of Ni, possibly by facilitating the formation of chemical bonding between Si in the matrix and the Ni nanochains. X-ray photoelectron spectroscopy (XPS) further shows that the excess Si from the dissociation of HSQ formed silicide-like chemical bonds with Ni that are robust to high temperature oxidation and protect the Ni nanostructures. Besides, the Ni-SiO<sub>x</sub> system showed 90% solar absorptance and a low thermal emissivity of 20% at 300 °C in air, compared to ~30% emittance of conventional coating at the same temperature. This technology helps to eliminate the problem of vacuum breaching and further reduces the fabrication cost of the solar selective coating. With a high solar absorptance, a low thermal emittance in the infrared region, and excellent anti-oxidation property, this type of selective solar thermal absorber is promising for applications in future generations of CSP systems.