Using semiconductor components in power electronics (static converters) circuits has many objectives: high frequency switching, high current, high voltage, increase their operating temperature and reduce the volume of equipment. However, working with these conditions for semiconductor components increases the electromagnetic interferences (EMI) that can have a significant impact on the neighboring systems. This paper presents a study of the ageing (electrical and/or thermal) of Power Radio Frequency Transistors RF N-LDMOS effect on conducted electromagnetic interferences emitted by DC-DC converter circuits. Conducted electromagnetic interference characterizations are performed for circuits using safe and aged power RF N-LDMOS. Through examination of experimental results, an accelerated ageing effect on the LDMOS transistor shows variations on conducted electromagnetic disturbance in common and differential mode voltage.