In this paper, power added efficiency (PAE) and linearity characteristics of AlGaN/GaN HEMTs are compared with those of high-voltage GaAs pseudomorphic HEMTs. Devices with different gate widths are characterized for their power output, gain, PAE and linearity performances as a function of bias current and source and load impedance. When compared to the source/load power matched condition, source tuning provides a significant improvement in the linearity without compromising the PAE performance, whereas, load tuning results in a substantial reduction in PAE to gain a marginal improvement in linearity. For the GaN devices, a maximum power added efficiency (PAE) of 58.5% for class AB operation and a maximum third order intercept point (IP3) of 42.7 dBm for class A operation were obtained. When operated at similar dc power dissipation conditions under class AB bias, similar output power and efficiency were measured for the GaN and GaAs devices, but three times higher power density and better linearity were measured for the GaN devices compared to the GaAs devices. (C) 2009 Elsevier Ltd. All rights reserved.