This article concerns a pseudo-Schottky diode Palladium/Indium-Phosphide (Pd-InP) gas sensor. The catalytic activity of such a palladium layer coupled with a pseudo-Schottky structure enables the measurement of very low concentrations of two highly oxidant gases: nitrogen dioxide (NO2) and ozone (O-3). The submission of the sensor to long O-3 exposures leads to a degradation of its sensor characteristics (response time, recovery time and sensitivity) due to oxidation of the palladium metallization by O-3. Therefore, to improve sensor lifetime and reduce drift, a methodology based on cyclic regeneration of the sensor's palladium surface (carbon monoxide (CO) reduction associated with thermal treatment) has been developed. The pseudo-Schottky gas sensor associated with this methodology exhibits reproducible responses, significant resolution and real time detection in the range of 20-100 ppb for NO2 and O-3. Moreover, a sensor exposed to 20 ppb of O-3 presented twice the response of the same sensor exposed to 100 ppb of NO2 (10.5 nA for 6.5 nA). Selectivity towards O-3, with this methodology, is demonstrated in the case of atmospheric pollution monitoring. (C) 2007 Elsevier B.V. All rights reserved.