An i-InGaP/n-In xGa 1 - xAs/i- GaAs step-graded doped-channel field-effect transistor (SGDCFET) has been fabricated and studied. Due to the existence of a V-shaped energy band formed by the step-graded structure, a large output current density, a large gate voltage swing with high average transconductance, and a high breakdown voltage can be expected. In this study, first, a theoretical model and a transfer matrix technique are employed to analyze the energy states and wavefunctions in the step-graded quantum wells. Experimentally, for a 1 × 80 μm2gate dimension device, a maximum drain saturation current density of 830 mAmm - 1 , a maximum transconductance of 188 mSmm - 1 , a high gate breakdown voltage of 34 V, and a large gate voltage swing 3.3 V with transconductance larger than 150 mSmm - 1 are achieved. These performances show that the device studied has a good potentiality for high-speed, high-power, and large input signal circuit applications.