AbstractA study of electrical properties and detection performances of the semi-insulating (SI) InP based detectors is presented. Detectors with a top P+ layer and a Schottky back contact give the charge collection efficiency about 90 % and an energy resolution 3.7% (FWHM) for 5.48MeV α-particles at 250 K. Detection of X-rays (122 keV and 60 keV) photons in temperature region 220–250 K is demonstrated. Multiple peaking observed during detection of photons is discussed.