Fluid sensor , comprising: A substrate having a top main surface region (110-A), wherein the top main surface region (110-A) of the substrate forms a common system plane of the fluid sensor, a thermal radiation emitter on the top main surface region (110-A) of the substrate , wherein the thermal radiation emitter comprises a semiconductor strip having a main emission surface region (122-C) for emitting a broadband thermal radiation (R) in a main radiation emission direction parallel to the system plane (110-A), wherein the thermal radiation emitter comprises a metallic cover layer which at least partially covers the main emission surface region (122-C) of the semiconductor strip , an optical filter structure on the top main surface region (110-A) of the substrate , wherein the optical filter structure comprises a semiconductor material and is configured to filter the broadband thermal radiation (R) emitted by the thermal radiation emitter and to provide a filtered thermal radiation (R 0 ) having a center wavelength λ 0 , a waveguide on the main top surface region (110-A) of the substrate , wherein the waveguide comprises a semiconductor material and is configured to guide the filtered thermal radiation (R 0 ) having the center wavelength λ 0 , wherein the guided thermal radiation (R 0 ) comprises an evanescent field component for interacting with the surrounding atmosphere comprising a target fluid, and a thermal radiation detector on the top main surface region (110-A) of the substrate , wherein the thermal radiation detector is configured to provide an detector output signal (S OUT ) based on a radiation strength of the filtered thermal radiation (R 0 ) received from the waveguide . A substrate having a top main surface region (110-A), wherein the top main surface region (110-A) of the substrate forms a common system plane of the fluid sensor, a thermal radiation emitter on the top main surface region (110-A) of the substrate , wherein the thermal radiation emitter comprises a semiconductor strip having a main emission surface region (122-C) for emitting a broadband thermal radiation (R) in a main radiation emission direction parallel to the system plane (110-A), wherein the thermal radiation emitter comprises a metallic cover layer which at least partially covers the main emission surface region (122-C) of the semiconductor strip , an optical filter structure on the top main surface region (110-A) of the substrate , wherein the optical filter structure comprises a semiconductor material and is configured to filter the broadband thermal radiation (R) emitted by the thermal radiation emitter and to provide a filtered thermal radiation (R 0 ) having a center wavelength λ 0 , a waveguide on the main top surface region (110-A) of the substrate , wherein the waveguide comprises a semiconductor material and is configured to guide the filtered thermal radiation (R 0 ) having the center wavelength λ 0 , wherein the guided thermal radiation (R 0 ) comprises an evanescent field component for interacting with the surrounding atmosphere comprising a target fluid, and a thermal radiation detector on the top main surface region (110-A) of the substrate , wherein the thermal radiation detector is configured to provide an detector output signal (S OUT ) based on a radiation strength of the filtered thermal radiation (R 0 ) received from the waveguide . <EOS>