This paper demonstrates the reduction of intra-winding capacitance in a high efficiency copper foil transformer. High efficiency transformer have low ac-resistance and low leakage inductance due to extensive interleaving of the transformer winding. Often high interleaving in a transformer winding leads to an increase in the intra-winding capacitance. This paper analyze how to estimate the intra-winding capacitance in a copper foil transformer. Two transformers are designed for a 2.4 kW, 50 kHz isolated dc-dc converter and presented in this paper. By changing the winding configuration, the intra-winding capacitance of the transformer has been reduced from 692pF to 150pF without increasing the leakage inductance and the ac-resistance. Efficiency measurement for the 2.4 kW converter utilizing the proposed low intra-winding capacitance transformer is also presented in this paper.