The energy resolution of CdTe detectors typically deteriorates in several tens of minutes due to the polarization effect at 30degC. In this paper, the energy resolutions were evaluated at 30degC and 35degC, and the periodic bias reset technique was investigated as a way to stabilize the detector performance. Two different bias reset circuits were used, one was an exponential voltage change type and the other was a linear voltage change type. The 500 V bias with 0.5 s to 60 s reset durations and 1 min to 20 min reset intervals was applied to 1 mm thick CdTe detectors. It was found that the 0.5 s reset duration and 5 min reset interval were able to stabilize the detector performance at 35degC.