A kinetic model of photoablation with the nanosecond pulses of an excimer laser, based on the so‐called moving interface, is presented. The rate of the ablating interface is assumed to be v=k(I−It) when the intensity I exceeds the threshold intensity It. The intensity reaching the interface I attenuated by the absorption of the products is I0e−βx, where x is the position of the interface. The ablation rate constant k of the polymer and screening coefficient β of the gas products are evaluated for each polymer and wavelength, by fitting the etch curves obtained precisely with our quartz crystal microbalance technique (as well as the literature data). The etching of polyphenylquinoxaline, a thermostable polymer, at three wavelengths (193, 248, and 351 nm) is given as an example.