An ignition coil unit comprising within an electrically insulating casing (31) an ignition coil (A) and a packaged power switch circuit (E). The packaged power switch circuit (E), which comprises a plurality of electric and electronic components (F) hermetically sealed within a mold resin (G) to form a single compact unitary piece, is disposed within a power switch cavity (31d) of the casing (31). An aluminum heat dissipating plate (30) may be attached at its first end (30a) to said packaged power switch circuit (E) in a thermally conductive relationship and exposed at its second end (30b) to the exterior of said casing (31).