-This paper shows by simulation that a shunt short -circuited /4 line placed across the drain terminals of a microwave MESFET amplifier significantly improves both the IM3/C and 2-tone PAE performance by a maximum of 14dB and 3%(from 24.5% to 27.5%), respectively. Practical confirmation with both WCDMA and GSM-EDGE input signals is obtained with a microstrip amplifier at 2GHz demonstrating an average improvement in ACPR of 12.5dB and a reduction in EVM from 5.0% to 1.3% respectively. The technique is novel, simple and practical and will be of direct interest to designers of base station amplifiers.