In this paper, a single-layer guided-mode resonance (GMR) filter based on a free-standing silicon-nitride membrane suspended on a silicon substrate is achieved by using bulk-micromachining technology. Both of grating and waveguide structures without a lower-cladding layer, i.e., substrate, are fabricated simultaneously on a silicon-nitride membrane. The device can be used as a transmission bandstop filter with the advantages of simple structure, high efficiency, and feasibility to integrate with other optoelectronic elements into a microsystem chip. The design consideration, fabrication procedures, and measured spectral response are shown in this paper. Moreover, by stacking two proposed devices,Δλ of the stopband at a transmission below 10% is 5.06 nm.