This work presents the performance of a radiation detector based on LEC semi-insulating GaAs with Au/Zn Schottky contact at variable temperature. The roles of the shaping time of a linear amplifier and operating voltage were studied. The performance of the radiation detector was calculated from pulse height spectra of 59.5 keV (241Am) and 122.1 keV (57Co). The optimal reverse bias voltage of the radiation detector, shaping time of the linear amplifier and temperature of detector were investigated. The best charge collection efficiency of 98.2% at 303 K, relative energy resolution in FWHM 19.8% for 59.5 keV and 10.7% for 122.1 keV at 253 K were obtained.