Investigation has been conducted to characterize the intrinsic performance of a SDD (silicon drift diode) based gamma detector under various conditions. The prototype detector consists of an array of seven hexagon-shaped SDDs that is optically coupled to a single slab of a scintillator. The length of active area ofthe SDD sensor is 15.2 mm in diameter. The detector unit (SDD array, scintillator and preamplifier circuits) was operated in a cooling chamber. And the typical operating temperature of the chamber was set to -20°C. In addition, Nitrogen gas was supplied to the detector unit to prevent condensation. The drift time was measured with a LED pulse generation device. And the longest drift time was measured 4.6 μsec from the edge of the sensor. The intrinsic energy resolution with a 55Fe source for direct x-ray conversion was 3% at 5.9 keV peak. For indirect conversion, i.e., photon detection, the energy resolution was 7.9% and 8.2% with 13 μsec and 2.71 μsec shaping time for the CsI(TI) and the NaI(TI), respectively. For indirect conversion measurement, the temperature was set to -20°C and lxlxlcm3 cube scintillator was directly coupled to a sensor. For intrinsic spatial resolution measurement with a hole-phantom (3 holes with 2mm in diameter), the x and y directional profiles at a center hole were 2.2 and 2.1 mm in FWHM, respectively. It has been observed that the intrinsic performance of the SDD prototype is so promising that the technology is highly feasible to be used as a gamma ray detector with many advantages.