A planar transformer comprises a laminate substrate having an opening with metal traces wound thereabout forming a primary and a secondary winding, a core configured to fit inside the opening to enclose the laminate substrate. At least one heat sink fin is integrally formed with the top, bottom or both sides of the core. A method of forming a planar transformer comprises laminating a substrate having an opening with metal traces wound thereabout forming a primary and a secondary winding, fitting a core inside the opening, and enclosing the laminate substrate. One of the top, bottom or both sides of the core include one or more heat sink fins.