The selective and sensitive detection of gases with microsystems has been a major challenge for some time. Resistive measurement techniques are often used, though their signal values often exhibit age-related drift and poor selectivity. A novel, monolithic photoacoustic gas sensor (PAS) from the Technical University of Dortmund that can be manufactured for microsystems technology is different: It detects target gases with high precision and selectivity. The underlying photoacoustic measuring principle works as follows: When a gas sample in a measuring cell is irradiated by a pulsed light source, the gas molecules absorb the light and the sample heats up. Given the measuring cell’s constant volume, the result is pressure waves whose frequency matches the modulation frequency of the light source. These pressure waves—that is, the photoacoustic signal—can be detected with elements sensitive to sound, such as microphones. The signal amplitude correlates with the degree of absorption, shedding light on the concentration of gas in the measuring cell. Due to the design of the invention, no photodetector is necessary. The universal manufacturing principle of a PAS based on an SOI wafer makes it possible to monolithically integrate all the necessary sensor components. With these types of sensors, all gases can be detected that exhibit strong absorption under IR, such as carbon dioxide and methane.