We report on the fabrication and characterization of quantum-doped graded-like channel heterojunction field-effect transistors (HFETs) by molecular beam epitaxy (MBE) using a multiple pulse doping technique. The extended equations describing the piecewise doping profiles have been developed to derive the transconductance and second-harmonic to fundamental ratio. It is found that the thickness of depletion width dominates the maximum transconductance and the high doping gradient offers the device linearity. Two HFETs with different doping gradients have been fabricated to elucidate this concept. We obtain the maximum extrinsic transconductance of 165 . Both have broad plateaus on their transconductance versus gate-to-source voltage profiles. Further, the devices exhibit a gate-to-drain and a drain-to-source breakdown voltage larger than 25 V. The very small output conductance and good pinch-off characteristics indicate good confinement of the electrons in a quantum-doped channel.