© 2019 The Japan Society of Applied Physics. Organic field-effect transistors (OFETs) containing a 9,10-diphenylanthracene (DPA) layer were fabricated with oxidized silver (AgOx) electrodes, and their electrical properties were investigated. The OFET structure consisted of heavily doped n-type Si wafers (SiO2) as the gate dielectric layer, fabricated silver source-drain electrodes oxidized by ultraviolet-ozone surface treatment, and finally the DPA layer. In spite of the large ionization potential of the DPA layer (∼5.8 eV), a high mobility (∼1.1 cm2 V-1 s-1)) was measured for OFETs with a AgOx layer oxidized for 600 s, which resulted in a reduction in the contact resistance to 8.0 kΩ cm. The observed behavior was attributed to the fact that the AgOx layer with its high oxidizability contributed to hole injection by oxidizing the surface of the DPA layer. Moreover, hole injection was more strongly enhanced by the presence of Ag2O rather than AgO.