The authors report on the improved microwave performance of short AlGaN/GaN doped channel heterostructure field effect transistors. These transistors with 0.25 mu m gates have a cutoff frequency f(T) up to 36.1 GHz (the highest reported value for a wide-bandgap semiconductor) and a maximum oscillation frequency f(max) similar or equal to 70.8 GHz. This value of f(T) is the highest value reported for any wide-bandgap semiconductor device.