When students first encounter energy bands in semiconductors, and how the properties of simple semiconductor devices such as the "p-n" junction diode depend on them, the concept can be a bit difficult to grasp. As part of an undergraduate physics course for non-STEM majors that includes semiconductors and simple devices based on the "p-n" junction, a gravitational analog of the device, using an inclined plane and ball bearings (Fig. 1), has helped students understand the concept. The model has also proved useful in introductory solid-state physics and semiconductor device courses.