Microwave oscillations in double barrier GaAs‐AlxGa1-xAs resonant tunneling heterostructures have been investigated. In this letter an approach is presented to obtain stable, dc current‐voltage (I‐V) curves by using a damped microwave circuit to prevent device oscillations which distort the measured I‐V curve. Numerical calculations confirm that if oscillations are allowed while making an I‐V measurement, the measured current is the sum of the stable, bias current plus the rectified component of the oscillating current. In addition, the first room‐temperature high Q microwave oscillations in resonant tunneling heterostructures are reported, as opposed to relaxation oscillations previously published. At 77 K, the highest power levels and efficiencies that have been achieved to date are presented.