A 170-mW class GaAs Power MESFET and a 10-mW class MMIC pre-amplifier operating at very low drain bias have been developed for use in personal handy phones (PHP). The MESFET provided P0(1dB)22.5 dBm, ηadd38.8% at VDS3 V with IDS0.14 A (0.4 IDSS) at 1.9 GHz, and also provided P0(1dB)22.4 dBm, ηadd32.6% at VDS2 V with IDS0.24 A (0.6 IDSS). The MMIC using the same MESFET structure had a linear power gain of 13 dB, a linear output power of more than 10 dBm, and P0(1dB)13.7 dBm, ηadd24.3% at VDD3 V with ID30 mA at 1.9 GHz. The MESFET had a buried p-layer and our improved LDD n self-aligned structure both of which were optimized so as to satisfy a high V(BR)GDO of more than 10 V, a minimized bias dependence of S-parameters and low VK of less than 0.5 V.