A corona igniter 20 includes an electrode gap 28 between the central electrode 22 and the insulator 32 and a shell gap 30 between the insulator 32 and the shell 36. The gaps 28, 30 are filled with a filler material 40 to prevent corona discharge 24 in the gaps 28, 30 and to concentrate the energy at a firing tip 58 of the central electrode 22. The filler material 40 may be electrically insulating or conductive. The shell gap width ws may be greatest at a shell lower end 92. The shell gap 30 may also be in a turnover region between a shell upper end 44 and the insulator 32, in which case the filler material 40 is injection molded around the turnover region. During operation of the igniter 20, the filler material 40 provides a reduced voltage drop across the gap 28, 30.