The 'DLC-GFET', a graphene field effect transistor with a diamondlike carbon (DLC) top-gate dielectric film, is presented. The DLC film was formed 'directly' onto the graphene channel without forming passivation interlayers using our original photoemission-assisted plasma-enhanced chemical vapor deposition (PA-CVD), where the plasma was precisely controlled by photoemission from the sample with quite low electric power to minimize plasma damage to the channel. The DLC-GFET exhibits clear ambipolar characteristics with a slightly positive shift of the neutral points (Dirac voltages). Relatively high transconductances were obtained as 14.6 (8.8) mS/mm in the n (p) channel modes, respectively, with a thick gate dielectric of 48 nm and a long gate length of 5 μm, promising vertical scaling-down to improve the high-frequency performance. The positive shift of the Dirac voltage is due to unintentional hole doping from oxygen species in the DLC film into the graphene channel, promising a minute modulation doped structure with oxygen to overcome high resistance in the access region. Hence, a DLC film deposited by PA-CVD is a candidate for the gate dielectric on graphene.