We report low field transport properties ofn‐channel GaAs‐AlxGa1−xAs heterojunction field‐effect transistors. Studies of the Shubnikov‐de Haas effect confirm that the devices are insulated‐gate field‐effect transistors, with AlxGa1−xAs as the gate insulator. The channel mobility increases with density following &mgr;2∼n&ggr;, with &ggr; varying from 0.45 to 1.4. &mgr; = 1.2×105cm2/V sec at 78 K and 3.6×105cm2/V sec at 4.2 K are observed atn∼4×1011/cm2.