We present the design and the characterization of a polycrystalline silicon (Si)-based photonic crystal (PhC)-suspended membrane, working in the mid-infrared wavelengths. In order to facilitate transmission measurement, the PhC membrane is released by removing the underneath Si substrate. Around 97% reflection and 3% transmission at 3.58-μm wavelength are measured at room temperature. Characterization is also done at 450°C and it reveals that the peak reflection of the PhC membrane shifts by 75 nm to higher wavelengths. This corresponds to a linear wavelength shift of and the thermo-optic coefficient is calculated to be . By altering the dimension of the PhC air holes, it is also shown that such a thermo-optic effect is compensated.