The silicon-photomultiplier (Si-PM) is a promising photodetector for the development of new PET systems due to its small size, high gain and relatively low sensitivity to the static magnetic field. One drawback of the Si-PM is that it has significant temperature-dependent gain that poses a problem for the stability of the Si-PM-based PET system. To reduce this problem, we developed and tested a temperature-dependent gain control system for the Si-PM-based PET system. The system consists of a thermometer, analog-to-digital converter, personal computer, digital-to-analog converter and variable gain amplifiers in the weight summing board of the PET system. Temperature characteristics of the Si-PM array are measured and the calculated correction factor is sent to the variable gain amplifier. Without this correction, the temperature-dependent peak channel shifts of the block detector were -55% from 20 °C to 35 °C. With the correction, the peak channel variations were corrected within ±8%. The coincidence count rate of the Si-PM-based PET system was measured using a Na-22 point source while monitoring the room temperature. Without the correction, the count rate inversely changed with the room temperature by 10% for 1.5° C temperature changes. With the correction, the count rate variation was reduced to within 3.7%. These results indicate that the developed temperature-dependent gain control system can contribute to improving the stability of Si-PM-based PET systems.