The interface structures of single quantum wells grown on vicinal (100) substrates with a controlled offset 0.2° are studied by cathodoluminescence microscopy. Bright and dark stripe patterns are periodically observed in monochromatic images of the single quantum wells and the stripes replicate stair‐like stepped interfaces. It is further shown that the observed terrace width is several times larger than the average interstep distance of monolayer steps calculated from the offset angle and that the step height is not one monolayer. Based on the results, a new interface structure model has been proposed that takes the offset angle into account. Finally, it is shown that employing growth interruption during epitaxial growth as an interface smoothing technique has limitations.