Effects of operating temperature and postdeposition annealing, as well as gas concentration and flow rate, on the response characteristics of the lead phthalocyanine sensor are investigated in this work. A simple model based on the gas adsorption/desorption kinetics was developed; it predicts that the reciprocal of the response time is proportional to both NO2 concentration and gas flow rate, but decreases with operating temperature. From the temperature dependence of the reciprocal of response time, the activation energy of the adsorption process, E(a), and that of the desorption process, E(d), can be calculated. It is also found that heat treatment of the lead phthalocyanine film in air at 250 degrees C for 3 h will reduce the activation energies, and lead to faster sensor response.