In the letter we present DC and microwave characteristics of three different QWITT structures. A peak output power of ∼ 1 mW in the frequency range 2–8 GHz has been obtained. This is the highest output power obtained from any quantum-well oscillator at any frequency. We will show that, for the same quantum-well structure, by systematically increasing the length of the depletion region (i.e. the drift region) on the anode side of the device, a corresponding increase in the specific negative resistance and output power is obtained. The significant increase in output power clearly suggests that the intrinsic device characteristics have been improved through the use of a drift region. This is in keeping with small-signal analysis for the QWITT diode, which predicts an improvement in the RF performance of the device with the use of an appropriate drift region length for a particular frequency of operation.