We present a back gated 2DEG (two‐dimensional electron gas) structure using low‐temperature grown (LTG) GaAs as a barrier layer between the back gate and the undoped GaAs channel. The sheet concentration of the 2DEG can be linearly varied from full depletion up to 3×1011cm−2at 12 K. When this charge modulation is modeled by a simple parallel plate capacitor, we find that the distance between the plates is approximately equal to the channel thickness rather than the actual spacing between the 2DEG and the back gate (which is the channel thickness plus the LTG GaAs thickness). We explain this behavior by observing that the leakage path is limited by the triangular barrier to conduction formed at the interface between the LTG GaAs defect band and the undoped GaAs channel conduction band. ©1995 American Institute of Physics.