Geothermal piles are subjected to daily and seasonal cyclic temperature changes during their life spans. These temperature changes (heat cycles) induce cyclic expansion/contraction along the soil–pile interface that may affect interface properties such as shear strength. A series of direct shear tests was conducted using a temperature controlled direct shear test apparatus to evaluate the effects of heat cycles on soil–pile interface strength. The interface temperature was cycled between 24 ° C and 34 ° C to simulate the real thermal conditions that an energy pile may experience. Non-cyclic and cyclic thermal loading were applied under different stress states and histories. It was found that the shearing behavior of interface under thermal loading is described through thermally induced changes in Mohr–Coulomb's parameters of the interface. Moreover, the thermally induced changes in interface strength are mainly controlled by the soil stress state and the soil stress history.