We report on DC and microwave characteristics for high electron-mobility transistors (HEMT's) grown on Si substrates by metal-organic chemical vapor deposition (MOCVD). Threshold voltage (V
th) distribution in a 3-in wafer shows standard deviation of V
th (σV
th) of 36 mV with V
th of -2.41 V for depletion mode HEMT's/Si and σV
th of 31 mV with V
th of 0.01 V for enhancement mode, respectively. The evaluation of V
th in a 1.95×1.9 mm
2 area shows high uniformity for as-grown HEMT's/Si with σV
th of 9 mV for V
th of -0.10 V, which is comparable to that for HEMT's/GaAs. Comparing the V
th distribution pattern in the area with that for annealed HEMT's/Si, it is indicated that the high uniformity of V
th is obtained irrelevant of a number of the dislocations existing in the GaAs/Si. From microwave characteristic evaluation for HEMT's with a middle-(10~50 Ω·cm) and a high-(2000~6000 Ω·cm) resistivity Si substrate using a new equivalent circuit model, it is demonstrated that HEMT's/Si have the disadvantage for parasitic capacitances and resistances originated not from the substrate resistivity but from a conductive layer at the Si-GaAs interface. The parasitic parameters, especially the capacitances, can be overcome by the reduction of electrode areas for bonding pads and by the insertion of a dielectric layer under the electrode, which bring high cut-off frequency (f
T) and maximum frequency of operation (f
max) of 24 GHz for a gate length of 0.8 (μm). These results indicate that HEMT's/Si are sufficiently applicable for IC's and discrete devices and have a potential to be substituted for HEMT's/GaAs
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