A new approach is described for utilizing atomic layer-deposited alumina as a gas–solid stationary phase medium for microfabricated gas chromatography columns. After atomic layer deposition (ALD) of aluminum oxide, a chloroalkylsilane is utilized to functionalize the oxide surface to improve peak symmetry and retention times. Semipacked columns (1 m-long, 190 μm-wide, 180 μm-deep with 20 μm-embedded circular micropillars) were utilized for validation of this newly developed approach. ALD-treated/silane-functionalized columns efficiently separated a multicomponent sample mixture and yielded 4200 plates per meter. The ALD-based stationary phase is found to be stable after multiple injections and at high operating temperatures. The proposed method facilitates a simple and wafer-level coating scheme that provides a highly controllable film thickness. The inherent properties of atomic layer deposition provide an easy route to coat very challenging microfabricated column designs.