Al0.2Ga0.8N/GaN HEMTs have been fabricated from MOCVD-grown epilayers on (0 0 0 1) sapphire substrates. DC current densities from 0.5 to similar to1 A/mm were achieved for gate lengths ranging from 0.75 to 0.1 mum. A maximum transconductance of 207 mS/mm was measured for short gate length devices. From s-parameter measurements, f(t) of 59 GHz and f(max) of 90 GHz were extracted. Load pull results from 0.25 x 150 mum(2) gate dimension devices indicated an output power density of 2.75 W/mm at 3 GHz and 1.7 W/mm at 10 GHz. Small signal modeling of the measured s-parameters is also presented. (C) 2002 Elsevier Science Ltd. All rights reserved.