Photoelectron-spectromicroscopy experiments unexpectedly revealed a reacted phase for Ge overlayers on GaSe. This finding is in sharp contrast with the notion that this interface is an ideal Schottky system, whose band discontinuities, for example, are determined by the Anderson rule-and with the widespread belief that most III-VI-based interfaces behave like Schottky systems. After this result, to the best of our knowledge, no heterojunction is known that matches the requisites of an ideal Schottky system.