Photoresist removal was studied using single-crystal silicon samples mounted on a ceramic heater in an UHV compatible chamber. The photoresist-coated sample was exposed to an ozone-oxygen mixture at atmospheric pressure and at a flow rate of 4 sl/min. Resist removal rate was measured using in situ laser interferometry. The removal rate was found to be a linear function of ozone concentration with a slope of 0.82 nm/s/unit mass fraction at a substrate temperature of 200 degrees C. The linearity is consistent with a simple chemical rate model. Typical photoresist removal rates at a mass density fraction ozone concentration of 0.09 ranged from 2.5 to 13 nm/s for substrate temperatures ranging from 150 to 300 degrees C, respectively. These rates are comparable with those observed by others. Over this temperature range, removal rates follow standard Arrhenius behavior from which an activation energy of 5.2 kcal/mol was determined. This value is similar to the known activation energy of 6.0 kcal/mol for the thermal dissociation of ozone leading us to conclude that thermal dissociation is the rate limiting step in the process. Our result is also significantly lower than reported previously and may be more accurate since the substantial shrinkage of photoresist with temperature was accounted for in these results. Additionally, the combination of concentration and temperature information is shown to lead to an effective chemical reaction rate constant for the removal of photoresist with ozone.