SPECT (single-photon emission computed tomography) is used as a tool in diagnosing the physiological functions of organs. A drawback of SPECT is the low spatial resolutions about 1 cm. Radiation detectors used for SPECT are required for high spatial resolutions to find small lesions. In this study, a signal processing technology was developed to improve the spatial resolutions of TlBr pixelated semiconductor radiation detectors with an anode pixel electrode, a guard electrode, and a cathode electrode. The radial interaction position in the anode pixel for the incident gamma ray was determined by taking the anode to guard electrode signal ratio. In addition, the depth of interaction of the incident gamma ray was determined by taking the cathode to anode signal ratio. The energy resolution of the TlBr pixelated detector was improved by selecting the events occurred near the cathode surface region and in the central region of the anode pixel.