A miniature oxygen sensor makes use of paramagnetic properties of oxygen gas to provide a fast response time, low power consumption, improved accuracy and sensitivity, and superior durability. The miniature oxygen sensor disclosed maintains a sample of ambient air within a micro-channel formed in a semiconductor substrate. O2 molecules segregate in response to an applied magnetic field, thereby establishing a measurable Hall voltage. Oxygen present in the sample of ambient air can be deduced from a change in Hall voltage with variation in the applied magnetic field. The magnetic field can be applied either by an external magnet or by a thin film magnet integrated into a gas sensing cavity within the micro-channel. A differential sensor further includes a reference element containing an unmagnetized control sample. The miniature oxygen sensor is suitable for use as a real-time air quality monitor in consumer products such as smart phones.