A novel MEMS-based tunable optical filter, an essential component for monitoring and reconfiguration of optical wavelength-division multiplexing networks, is presented. The device is based on a Fabry-Perot interferometer employing multiple solid-state silicon cavities and silicon-based dielectric Bragg mirrors. Tuning is achieved through thermal modulation of the resonator's optical thickness. It is fabricated as a free-standing membrane using silicon MEMS technology. The filter membrane is fixed by micromachined suspension arms, which thermally isolates it against the substrate. The present concept features low power consumption and fast thermal modulation. Light coupling to the filter array is realized by positioning of fibers and the filter chip in a micro-optical bench setup.