The crystalline quality of tensile strainedGa0.25In0.75Players grown on InP substrates was investigated. The samples were grown by metalorganic molecular beam epitaxy. Little or no relaxation was found inGa0.25In0.75Players which were up to 500 Å thick. The relaxation of layers less than 700 Å thick was isotropic, but thicker (bulk-like) layers relaxed anisotropically, with the main relaxation along the [11̄0] direction. Fully strained layers up to a thickness of 650 Å were obtained by employing strain compensation. Heterostructure field effect transistors (HFETs) incorporating a tensile 200 Å thickGa0.25In0.75Pbarrier were fabricated. A composite channel of compressive strainedGa0.3In0.7Asand lattice matched GaInAs was used to compensate the tensile strained barrier. The HFET channel was partially doped. A peak transconductance of 200 mS/mm was obtained in HFETs having a 1 μm long gate. The drain-source breakdown voltage was 10 V, and gate-drain breakdown voltage was 11 V. The unity current gain frequency,fT,and the maximum frequency of oscillation,fmax,were 23.5 and 50 GHz, respectively. Resonant tunneling diodes withGa0.25In0.75Pbarriers and aGa0.47In0.53Aswell were demonstrated as well. Peak to valley current ratios of 1.15 and 5 were obtained at room temperature and 77 K, respectively.