A quantum doped channel inserted between two wide-gap barriers was grown upon a n(+)-collector layer. We observe a behavior associated with held-effect transistors and real-space-transfer phenomena. In the case of FET behavior, doped channel FETs were fabricated using air-bridge gates with multiple piers. The available maximum extrinsic transconductance was 170 mS/mm with an output conductance of 0.3 mS/mm mm and a turn-on voltage of 1.4 V. The measured unity-current gain frequency and maximum available gain frequencies were 17 and 25 GHz, respectively. Experimental findings reveal that FETs fabricated using air-bridge gates with multiple piers really can overcome undesirable effects as it grown upon the n+-collector. In the case of real-space-transfer devices, the gate pad directly comes to rest upon the n(+)-collector layer. We observed FET characteristics with insignificant NDR behavior when the device is operated in the depletion mode. In contrast, interesting and clear NDR characteristics were observed when the device was operated in the enhancement mode. This supports the conclusion of real-space-transfer behavior in these devices.