Recently, intriguing physical properties have been unraveled in anisotropic layered semiconductors with the in-plane anisotropy often originates directly from the low crystallographic symmetry. However, little has been known about the systems where the size effect dominates the anisotropy of electronic band structures. Here, applying both experiment and theory, we show that the anisotropic energy bands of monoclinic gallium telluride (GaTe) are determined by a strong bulk-surface interaction rather than geometric factors. Bulk electronic states are found to be the major contribution to the highest valence band, whose anisotropy is yet immune to surface doping by potassium atoms. Further analysis indicates the weakened bulk-surface interaction gives rise to an inverse anisotropy of hole effective masses and the strong interlayer coupling induces a direct-indirect-direct band gap transition at transfer from mono- to few-layer GaTe. Our results thus pave the way to future applications of anisotropic layered semiconductors in nanoelectronics and optoelectronics.
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