We report markedly different transport properties of ABA- and ABC-stacked trilayer graphenes. Our experiments in double-gated trilayer devices provide evidence that a perpendicular electric field opens an energy gap in the ABC trilayer, while it causes the increase of a band overlap in the ABA trilayer. In a perpendicular magnetic field, the ABA trilayer develops quantum Hall plateaus at filling factors of u = 2, 4, 6... with a step of Delta u = 2, whereas the inversion symmetric ABC trilayer exhibits plateaus at u = 6 and 10 with 4-fold spin and valley degeneracy.
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