InGaAlAs epilayers lattice matched to an InP substrate are grown by molecular beam epitaxy with band gap energies varying in the range 0.8–1.42 eV. TheI–V/C–Vcharacteristics of the Schottky diodes fabricated on InGaAlAs/InP heterostructures are investigated in the temperature range 80–300 K to study the variation of barrier heights with the Al mole fraction in the alloy. It is noted that at room temperature due to the dominance of thermionic emission the Schottky characteristics are not observable on low Al fraction structures, primarily because of the low metal–semiconductor barrier and low heterostructure barrier potentials. However, at 80 K the potentials are high enough to provide measurable characteristics. For an Al mole fraction of 0.23, the band lineup of the InGaAlAs/InP heterostructure changes from type I to staggered type II. Also, for the band gap engineered InGaAlAs alloys, the variations of mobility and doping concentration in the temperature range 80–400 K are presented as a function of the Al mole fraction in the alloy.