Super regenerative detectors using a resonant tunneling diode (RTD) were fabricated and investigated for ultra-high frequency detectors. A key point is to use the RTD super regenerative detector for detecting much higher frequencies than the free-running oscillation frequency of the detector. This is possible owing to the superior high frequency characteristics of the RTDs. This has various advantages, such as circuit simplicity, easy design, and low power consumption. Clear detection of 50 GHz signal was demonstrated with a super regenerative detector which has 1.5 GHz free-running frequency. Moreover, detailed experiments revealed that the frequency dependence of the detection efficiency is smooth, and the harmonic frequencies have no effect. This is advantageous for high frequency detection.