Abstract: Gases can be selectively detected by the utilization of a infrared spectrometer via their specific absorption in the infrared spectral range. The sensor of the present invention is developed for continuously controlling a gaseous stream or a space filled with gas with the sensor being a single-piece shaped part manufactured as a microstructured body. The space filled with gas to be tested is between a mirror grating and entrance and exit slits for IR-radiation. The sensor is compact and robust, suitable for portable instruments, and can be manufactured at low cost and in large numbers. The sensor can also be made of metal and can be used even at an increased temperature. By using the sensor of the present invention, the safety of systems in which flammable, toxic or other gases are contained or may occur can be considerably increased in an economic manner.