All-optical modulation based on the photothermal effect of two-dimensional (2D) materials shows great promise for all-optical signal processing and communication. In this work, an all-optical modulator with a 2D PtSe 2 -on-silicon structure based on a microring resonator is proposed and demonstrated utilizing the photothermal effect of PtSe 2 . A tuning efficiency of 0.0040 nm · mW − 1 is achieved, and the 10%–90% rise and decay times are 304 μs and 284 μs, respectively. The fabricated device exhibits a long-term air stability of more than 3 months. The experimental results prove that 2D PtSe 2 has great potential for optical modulation on a silicon photonic platform.