Nitride-based GaN/In0.12Ga0.88N heterostructure field effect transistors (HFETs) with semi-insulating Mg-doped GaN current blocking layers were successfully fabricated. The as-grown layers exhibited a very smooth surface. The DC characteristics of these HFETs were substantially improved over those previously reported. Devices with a 0.75 Pm gate length showed a maximum drain current (I-DS) of 421 mA/mm, and a maximum g(m) of about 85.6 mS/mm at V-GS between -0.5 and -3V. The device which had a very good pinch-off with source-drain (S-D) leakage current was negligibly small, in the range of 10(-1)-10(-2) mA/mm. The RF characteristic of devices showed the current gain cutoff frequency, f(T), was 7.45 GHz and the maximum oscillation frequency, f(MAX), was 12.36 GHz. (C) 2004 Elsevier B.V. All rights reserved.