In this work, properties of non-evaporable getter (NEG) films prepared on stainless steel substrates by magnetron sputtering were investigated. Changes of the sample surface during thermal activation were studied by means of secondary ion mass spectroscopy (SIMS). Static SIMS observation of a superficial layer as well as dynamic profiling of the surface region were performed. Two samples of the same Ti:Zr:V stoichiometry were investigated following two different procedures of thermal activation. Step-by-step heating up to 320 °C (as model activation) and direct long time heating to 240 °C (continuous thermal activation) were applied. The SSIMS measurements are highly surface sensitive and reflect changes of the superficial oxide layer covering air-exposed surfaces during activation. To compare the final states of activation, depth profiles of surface layers have been used as well. Molecular ion intensity ratios MX +/M + (X=O, H; M=Ti, Zr, V) have been considered to be directly coverage-sensitive and were monitored during the processes. The results were checked by comparison to corresponding XPS experiments.