Pentacene thin-film transistor with high-κ ZrLaO gate dielectric has been fabricated for the first time. After treating the dielectric in a fluorine plasma, the carrier mobility of the transistor can be greatly improved to 0.717 cm 2 /V·s, which is more than 40 times that of one without plasma treatment. The major reasons should be larger pentacene grains and fewer traps in the device with gate dielectric passivated by the fluorine plasma. AFM confirms that relatively large and high pentacene islands form on the plasma-treated dielectrics in the initial growth stage, and the growth pattern obviously follows the Vollmer-Weber growth model. Furthermore, the surfaces of the dielectrics with different plasma treatment times are investigated by AFM, XPS and contact-angle measurement to reveal the mechanism / effects of the fluorine incorporation. Lastly, after exposure to atmosphere without encapsulation for 6 months, all the devices still display good transistor characteristics.