3D-LSI is a promising technology to increase transistor density as device scaling becomes more difficult. It also enables us to reduce power consumption and improve performance through wire length reduction. However, 3D-LSI has more serious thermal problems than non-stacked chips. Therefore, thermal management is necessary to maintain the temperature at the normal level in 3D-LSI. In this paper, we focus on the factor of 'ease of temperature rise' that varies depending on the position inside the 3D-LSI and propose an approach to incorporate this factor as the 'Position Weight' into the thermal management algorithm. Tasks are migrated from one processing element (PE) to another PE by considering both position weight and the temperature so as to suppress the maximum temperature. Using this approach, we developed an algorithm to suppress the maximum temperature inside the chip without changing the total amount of heat generated. Simulation verification was conducted using a commercial thermal analysis software. Results showed that our approach enabled us to reduce the maximum temperature in the chip by more than 15°C over the conventional techniques, while maintaining the performance.