The formation of quantized energy states in ultrathin layers of indium oxide (In2O3) grown via spin coating and thermally annealed at 200°C in air is studied. Optical absorption measurements reveal a characteristic widening of the optical band gap with reducing In2O3 layer thickness from ≈43 to ≈3 nm in agreement with theoretical predictions for an infinite quantum well. Through sequential deposition of In2O3 and gallium oxide (Ga2O3) layers, superlattice-like structures with controlled dimensionality and spatially varying conduction band characteristics are demonstrated. This simple method is then explored for the fabrication of functional double-barrier resonant tunneling diodes. Nanoscale current mapping analysis using conductive atomic force microscopy reveals that resonant tunneling is not uniform but localized in specific regions of the apparent device area. The latter observation is attributed to variation in the layer(s) thickness of the In2O3 quantum well and/or the Ga2O3 barrier layers. Despite the nonidealities, the tremendous potential of solution-processable oxide semiconductors for the development of quantum effect devices that have so far been demonstrated only via sophisticated growth techniques is demonstrated.