We study the electronic transport properties of graphene nanoribbons (GNRs) on SiO2/Si with O-terminated (siloxane) or OH-terminated (silanol) surfaces. The channel length and SiO2 thickness are 9.91 and 0.45 nm, respectively. The GNR shows p-type conduction on both the SiO2/Si surfaces. More holes are injected from OH groups in the silanol SiO2 to GNRs. The on/off current ratio for both GNRs on SiO2/Si is 103–105, which is consistent with recent experiments, and smaller by a factor of 108 than those of freestanding GNRs. The ratio is even smaller on the p side for the silanol SiO2.