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Total ionizing dose (TID) strongly affects the single event transient (SET) sensitivity of a bipolar linear voltage comparator (LM139). The general rule that transistors in the non-conducting state are the most sensitive to SETs was verified, with some exceptions. The mechanisms responsible for those exceptions were identified and explained using circuit analysis. In the non typical behavior, a correlation of the degradation of the amplifier stages with the shape of the transient output signal was established. Following total dose exposure the SETs generally exhibit a reduction in amplitude due to the degradation of the slew rate. However, in some cases the transient signal is amplified because degradation of either the current source or of the current gain of some transistors forces the output transistor to the edge of conduction, so that it behaves like a voltage amplifier and amplifies the parasitic transient signal. Laser testing demonstrates that ASET sensitivity also is affected by TID degradation of transistors that are not directly hit by the laser.