In order to address the metal oxidation issue in cermet solar thermal absorbers at high working temperatures, we developed solution-processed plasmonic Ni nanochain-SiOx (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-Al2O3 selective solar thermal absorbers, which readily oxidize at 450 °C. Ni nanochains were embedded in SiOx and SiO2 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-SiOx 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.