The surface structure of magnetron-sputtered YBa₂Cu₃O₇ thin films has been investigated using an STM operated in air. Both c-axis and a-axis oriented films have been investigated. In the case of c-axis thin films, different types of step and plateau structures are observed depending on the deposition conditions and substrates used (SrTiO₃ and MgO), suggesting different growth behavior. In some cases, very regularly spaced parallel plateaus separated by steps are found, suggesting directional step flow; whereas in other cases, more complex surface structures with circular plateaus and screw dislocations are seen. In the case of a-axis growth, the substrate determines the grain orientation and results in a cobblestone appearance of the film surface. The tunneling conditions necessary for obtaining stable and reproducible images of the surface are discussed as well as attempts to correlate the deposition parameters with the resulting film surface structure.