In this paper the intermodulation distortion (IMD) behaviour of a 0.25 power PHEMT is investigated under several device operating conditions. An extensive experimental device characterisation, together with numerical simulations using suitable non-linear transistor models is carried out. Experimental data were compared with different transistor models in order to understand the effect of the various cell parameters on the device IMD 3 response. The data collected were applied in the design of a highly linear power amplifier family, covering different frequency ranges.