A suitable short-time test for analysis of long term stability is presented for the case of passivated NiCr thin film resistors revealing an aging characteristic which is not of Arrhenius type. Based on the in-situ measurement of resistance change during a continuous temperature rise, so-called temperature ramp curve, a well-defined correlation is found between the film stability and a characteristic temperature Tp where the temperature ramp curve exhibits a maximum. In this way, a reliable prediction of the long term stability can be made within only a few hours. The influence of the heating rate on the characteristic temperature Tp is shown. Furthermore, it is experimentally proved that the values of Tp are not essentially determined by the reversible resistance changes due to differential temperature coefficient of resistance, but indeed by irreversible aging processes.