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This paper presents a novel thermal tunable bulk-micromachined optical filter. The device has been achieved based on a Fabry-Perot interferometer employing a bulk silicon cavity and high-reflectivity coating (HRC). A dense boron doped silicon resistor has been used as the heater and the cantilever structure has been designed to provide a good thermal isolation. The tunable optical filter has been successfully fabricated using bulk micromachining technology. Tunability is realized by changing the refractive index of the bulk silicon cavity through heating resistor. The maximum wavelength tuning is about 17 nm with driving voltage less than 14 V. The filter linewidth was achieved a value of 0.29 nm and the Free Spectral Range (FSR) was 21.9 nm. The heating and cooling responding times are less than 50 ms.