We report novel current–voltage characteristics in an InP‐based resonant‐tunneling high electron mobility transistor (RTHEMT). This device incorporates a pseudomorphic InGaAs/AlAs/InAs resonant‐tunneling diode into the source of a nonalloyed ohmic contact InAlAs/InGaAs high electron mobility transistor. Both pronounced negative differential resistance and negative transconductance are observed at room temperature. Most significantly, a near‐flat valley current is obtained in the output current–voltage characteristics. This feature is achieved by the nonalloyed ohmic contact cap layer structure employed in the HEMT, which significantly reduces the parasitic resistance. The novel characteristics of RTHEMTs should lead to many attractive circuit applications. ©1995 American Institute of Physics.