This paper reports a case study about effects produced by the radiation Single Event Transient (SET) injection on a custom operational amplifier. SETs were injected in the operational amplifier transistors in order to evaluate their sensitivity to the radiation transient faults. The circuit was designed using a non-rad-hard AMS-CMOS 0.8μm process. In this case, simulation results allow us to identify the operational amplifier most sensitive transistors. This work will form the basis to further development of design techniques for radiation hard analog circuits.