Our research has clearly shown that semiconductor crystals generally possess facet-dependent electrical conductivity, photocatalytic activity, and light absorption and emission properties. Piezoelectric and magnetic properties also exhibit notable facet effects, implying that all other materials properties are also facet-dependent. Band gaps of semiconductor crystals contain size and surface components, in addition to crystal phases, and are tunable over a very large size range from quantum nanostructures to microcrystals. The new knowledge gained about semiconductor materials is possible largely from the growth of various semiconductor nanocrystals with a range of sizes and different particle shapes. Previous DFT calculations have suggested the presence of a thin surface layer in semiconductor materials with lattice plane-dependent bond length variations and bond direction deviations to give rise to changes in the band structure. Different degrees of band bending are used to represent barrier heights to charge transport across a particular surface or heterojunction interface. Using this facet-specific surface layer idea, all these observed semiconductor facet effects can be understood, including the optical facet effect, that all these effects arise from the same origin. In addition to more demonstrations of semiconductor facet effects by making new crystals with tunable shapes, which is always challenging to achieve, one important research direction is to experimentally show the presence of this surface layer. Recently, synchrotron XRD and high-resolution TEM characterizations have revealed the existence of the surface layer in Cu2O and MnS nanocrystals. Moreover, slight lattice differences in the crystal bulk also exist and should contribute to the observed facet effects. From thermodynamics consideration, shape-related lattice variations appear naturally when particles are synthesized, and thus should be universally present in ionic solids. Recognizing these semiconductor facts should explain some efficiency variations in solar cells, photocatalysts, and color changes in routine semiconductor growth. Enhanced materials performance is possibly utilizing the new knowledge.