Silicon-organic hybrid (SOH) modulators have garnered sustained interest due to their superior performance, such as low driving voltage and compact footprint. However, concerns regarding their reliability have greatly hindered the wide-spread deployment. Recent progress in molecular synthesis significantly improves the thermal stability of SOH modulators. However, the reliability in damp heat aging test hasn’t been reported. In this paper, we report on a thin-film SOH modulator with a half-wave voltage–length product (VπL) of 1.18 V·cm. The device’s frequency response extends beyond 33 GHz without degradation. After exposure to 85 °C and 85 % relative humidity for 1,000 hours without packaging, the electro-optic (EO) response of the modulator degrades by only 7.3 %. This demonstration may help resolve doubts regarding the durability of SOH modulators.