We propose the epitaxial graphene field-effect transistors (EG-FETs) with Al2O3 gate dielectric formed by metal oxidation on semi-insulating 6HSiC substrate. The Al2O3 gate dielectric layer was formed by thermally oxidizing a thin Al film at 500°C in an O2 ambient. The electrical characteristics of EG-FETs with Al2O3 gate dielectric have been investigated, which exhibits p-type behavior with the field effect mobility of 120 cm2 V-1 s-1. After the Al2O3 formation, the FWHM of G0 and D peaks in the Raman-scattering spectra increased, indicating degradation of graphene and thereby accounting for the low field effect mobility of the EG-FETs. This finding suggests that the optimization of post growth heat treatments, such as oxidation and metallization, should play a decisive role in tuning the quality of graphene and the performance of the device made thereof.