The GaAs and AlGaAs layers were grown by MBE (Molecular Beam Epitaxy). To improve the quality of n-GaAs layer, the substrate temperature and V/III flux ratio were varied. The best quality was obtained at $T_{sub}=600\circ\C$ and V/III = 10 measured by nude-ion guage for beam flux monitoring. Doping concentrations ranging from low $^*10^{16}cm^{-3}$ to high $^*10^{18}cm^{-3}$ was obtained by varying the Si-cell temperature from 1050℃ to 1250℃. The elecrical properties of the n-type GaAs layers were characterized by the Van der Pauw Hall measurement and their optical properties were by the photoluminescence measurement. The mole fractions of $Al_xGa_{l-x}As$ layers can be controlled in the range of x=0.026~0.594 at the Al-crucible temperature range of $T_{Al}=925\circ\C\sim1100\circ\C$. MESFETs having the gate length of 1 μm and the gate width of 100μm were fabricated on the MBE-grown GaAs layers and characterized. Saturation currents and transconductances of the devices at Vg = 0V were typically 40 mA, 180mS/mm respectively. The variation of the transconductance and the $I_{DSS}$ was in the range of ±16%. These data indicates the uniformity of the MBE-grown MESFET layer and the applicability to the Monolithic Microwave Integrated Circuits (MMIC).
