The design, fahrication,and experimental characteristics of a 100-GHz monolithic cascode HEMT oscillator are presented. A cascode pair of InAlAdInGaAs HEMT's has been used as the active cell to enhance the negative resistance so that more process tolerance can be achieved. The monolithic circuit oscillates around 100 GHz with an output power of 2 dBm at a drain bias voltage as small as 0.9 V. This is the first demonstration of cascode HEMT oscillators at W-band.