A gas sensor comprises a chamber configured to receive a gas; a light source configured to emit a light wave propagating through the chamber in an emission cone; a measurement photodetector and a reference photodetector, each configured to detect a light wave emitted by the light source and having passed through the chamber. The chamber extends between two transverse walls, arranged opposite one another and connected to one another by a peripheral wall extending therebetween, about a longitudinal axis (Z), and comprising a first reflective segment configured to receive a first portion of the emission cone to reflect it toward the measurement photodetector, thus forming a measurement cone converging toward the measurement photodetector. A second reflective segment of the peripheral wall is configured to receive a second portion of the emission cone to reflect it toward the reference photodetector, thus forming a reference cone converging toward the reference photodetector.