The crystalline quality of tensile strained Ga0.25In0.75P layers grown on InP substrates was investigated. The samples were grown by metalorganic molecular beam epitaxy. Little or no relaxation was found in Ga(0.)25In(0.75)P layers which were up to 500 Angstrom thick. The relaxation of layers less than 700 Angstrom thick was isotropic, but thicker (bulk-like) layers relaxed anisotropically, with the main relaxation along the [1(1) over bar 0] direction. Fully strained layers up to a thickness of 650 Angstrom were obtained by employing strain compensation. Heterostructure held effect transistors (HFETs) incorporating a tensile 200 Angstrom thick Ga0.25In0.75P barrier were fabricated. A composite channel of compressive strained Ga0.3In0.7As and 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 mu m long gate. The drain-source breakdown voltage was 10 V, and gate-drain breakdown voltage was 11 V. The unity current gain frequency, f(T) and the maximum frequency of oscillation, f(max),,,, were 23.5 and 50 GHz, respectively. Resonant tunneling diodes with Ga0.25In0.75P barriers and a Ga0.47In0.53As well were demonstrated as well. Peak to valley current ratios of 1.15 and 5 were obtained at room temperature and 77 K, respectively.