This paper presents how the leakage inductance influences the switching behavior of a hard-switched isolated full-bridge forward converter when it transitions from its ON to OFF state. Two sub-states are presented, and equations describing the current in the transformer primary winding is derived. It is presented that the dissipated turn-ON switching loss in the primary switches is highly influenced by an resonance frequency involving the leakage inductance. The calculations is verified by simulation and measurement, both performed when the converter is operated at 2:5kW output power.