Static metal–semiconductor contacts are classified into Ohmic contacts and Schottky contacts. As for dynamic metal–semiconductor contacts, the in-depth mechanism remains to be studied. We here define a “triboelectric junction” model for analyzing dynamic metal–semiconductor contacts, where a space charge region induced by the triboelectric effect dominates the electron–hole separation process. Through theoretical analysis and experiments, we conclude that the triboelectric junction influences the electric output in two aspects: (1) the junction direction determines the output polarity; (2) the junction strength determines the output magnitude. Both the junction direction and junction strength are closely related to the electron-affinity difference between the contact metal and semiconductor.