We report results of the characterization of a high throughput 3 in. MBE system which we have used to fabricate high quality, uniform modulation‐doped field‐effect transistors (MODFET’s). MODFET threshold voltage of 14.6% and hence Nd2product uniformity of 11.3% standard deviation across a 3 in. MBE wafer was achieved. MODFET’s with 77 K mobility over 100 000 cm2/V s were fabricated. Silicon was used as then‐type dopant of the (Al,Ga)As/GaAs heterostructures. Successful calibration of the Si cell temperature resulted in controlled doping in the range 1014cm−3to mid‐1018cm−3in GaAs. AlxGa1−xAs (x≂0.3) was also doped successfully up to 2.5 ×1018cm−3. Doping and thickness uniformity of 2% for both (Al, Ga)As and GaAs over the central 2.5 in. of 3 in. substrates was achieved using substrate rotation.