In this thesis we experimentally study the intrinsic charge transport properties in n-channel organic field-effect transistors and its disorder-induced suppression. We observe that certain molecular and crystal structures are beneficial for minimizing the disorder experienced by charge carriers and thus for studying the microscopic charge transport mechanisms of organic semiconductors in a field-effect configuration. Experiments on perylene derivatives show that disorder can be suppressed by attaching longer core substituents – thereby reducing potential fluctuations in the transistor channel and increasing the mobility in the activated regime – without altering the intrinsic transport properties. We further explore the influence of the dielectric environment on the charge transport properties using polymer gate dielectrics as well as electric-double layer gating with ionic liquids. In our field-effect transistors, we further observe an extremely low gate bias stress effect, i.e., the degradation of the source-drain current upon prolonged application of a gate bias potential.