the thermal sensors 17 it is advantageous when the present apparatus 10 comprises a suitable monitoring device which offers the possibility for visualizing the detected temperature data by means of display means 24 the present example visually shows in the display means 24 a first temperature curve 21 of a substrate 14 a second temperature curve 22 of another substrate 14 and a third temperature curve 23 of a third substrate not shown here the temperature curves 21 22 and 23 show the respective temperatures on the respective substrates 14 over a specific period of time it is described on the basis of the first temperature curve 21 in which phase the first substrate 14 is located at the beginning of the etching process the substrate 14 on which the first spring supported thermal sensor 17 is arranged has an initial temperature 21 a which is close to the temperature of the thermostatic work plate with the start of the stripping process the temperature on the substrate 14 rises to an equilibrium temperature 21 b the equilibrium temperature will occur when the temperature gradient occurring towards the work plate 13 is dissipating the reaction heat from the substrate 14 the equilibrium temperature remains virtually constant as long as the stripping process occurs in this substrate 14 once the substrate 14 has been stripped of photoresist the temperature will start to drop the start middle end or other suitable places of the decreasing flank of the temperature curve can be recognized as the end point of the stripping process 21 c the possibility for setting an optimal etching duration is given by suitable setting of.