Hybrid organic−inorganic nanocomposites have been synthesized through hydrolysis and co-condensation between (4-(amino-N,N-(diethoxydiurethano)propyltriethoxysilane)-2-methyl-4‘-nitroazobenzene (ICTES−Red 17) and tetramethoxysilane (TMOS). From the resulting sols, coatings a few microns in thickness can be deposited. It has been shown that the aging time of the sol and the thermal treatment of the coatings are both important to improve the second-harmonic-generation (SHG) response and its temporal stability. The hybrid coatings 4.2 μm thick, with a 50/50 ICTES−Red 17-TMOS molar composition, exhibit the highest nonresonant SHG response (d₃₃ = 150 pm/V, λ = 1.34 μm) reported up to now for sol−gel-derived NLO materials. Moreover, they also exhibit a good stability at 80 °C.