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A graphene transistor with a bottom-gate coplanar structure and an atomic layer deposition (ALD) aluminum oxide (Al2O3) gate dielectric is demonstrated. Wetting properties of ALD Al2O3 under different deposition conditions are investigated by measuring the surface contact angle. It is observed that the relatively hydrophobic surface is suitable for adhesion between graphene and ALD Al2O3. To achieve hydrophobic surface of ALD Al2O3, a methyl group (CH3)-terminated deposition method has been developed and compared with a hydroxyl group (OH)-terminated deposition. Based on this approach, bottom-gate coplanar graphene field-effect transistors are fabricated and characterized. A post-thermal annealing process improves the performance of the transistors by enhancing the contacts between the source/drain metal and graphene. The fabricated transistor shows an Ion/Ioff ratio, maximum transconductance, and field-effect mobility of 4.04, 20.1 μS at VD = 0.1 V, and 249.5 cm²/V·s, respectively. [ABSTRACT FROM AUTHOR]