A GaAs/n+‐In0.2Ga0.8As/GaAs doped‐channel field‐effect transistor structure has been fabricated and studied. A typical transistor performance with a threshold voltage of about −3.0 V and transconductance of up to 160 mS/mm is obtained in the lower gate‐source voltage (VGS<−1.0 V) regime. However, for some devices, the three‐terminal‐controlled N‐shaped negative‐differential‐resistance (NDR) behavior is observed at the saturation regime of current–voltage characteristics under higher gate‐source bias (VGS≥−1.0 V) condition. The interesting NDR phenomenon is believed to be attributed to the real‐space transfer and deep‐level electron trapping effect. ©1995 American Institute of Physics.