This investigation proposes InAlGaP/InGaAs camel-gate high-electron mobility transistors with inverted delta-doping layers (CAM-HEMTs). CAM-HEMTs with various gate metals, including Au, Pt/Au, Ti/Au, and Ni/Au, are investigated. The CAM-HEMT with the Ni/Au gate metal exhibits the benefits of a large gate voltage swing (3.6 V), a high two-terminal gate-source breakdown voltage (>20 V), no bell-shaped gate current and temperature-insensitive threshold voltages. These characteristics are attributable to the inverted delta-doping layer, the large conduction-band discontinuity of the InAlGaP/InGaAs heterojunction, the large bandgap of InAlGaP and the high camel-gate barrier with the Ni/Au gate metal.