Abstract: Thermal semi conductor is a mechanism for the control of conduction heat flux between two or more bodies with differing temperatures, promoting the unidirectional heat flux. It consists of composite slabs composed of materials with high and low thermal conductivity appropriately set, granting the thermal semi conduction. These slabs are able to displace allowing the contact between materials with high thermal conductivity respectively in order to promote higher heat flux or, in opposite, to displace facilitating the contact between materials with low thermal conductivity respectively to promote lower heat flux. The control of the heat transfer through the mechanism is defined by positioning the slabs appropriately. External devices can be used to promote the relative displacement of the slabs. On the other hand, an adequate design of the slabs can be used to promote or to avoid their thermal contact through thermal expansion or contraction.