An energy model has been used to calculate the minimum critical thickness in strained‐layer superlattices that is required to block threading dislocations. The model calculates the total change in the system energy that results from the presence of a bent dislocation segment at the strained interface. The calculations show that a threading dislocation has to overcome an energy barrier before gliding along the strained‐layer interface becomes favorable. The model predicts that the process of blocking threading dislocations by strained‐layer structures can be thermally activated.