Three types of conduction band extrema in the (000), (100), and (111) directions inkspace seem to determine many of the properties of the group 4 and group 3–5 semiconductors. Early experimental work on the pressure coefficients of the energy separations of these extrema from the valence band maximum energy, carried out on Ge (111), (000), (100), Si (100), and InSb (000), suggested that the three pressure coefficients might be independent of the specific element or compound in the group 4 and group 3–5 series. This work is discussed in detail, and the theoretical basis is briefly considered. All of the completed pressure measurements on these compounds are critically reviewed, and the correlation of unique pressure coefficients with specific band edges examined. It is demonstrated that pressure experiments can be planned to show up details of the band structure unavailable for study at atmospheric pressure. Particular attention is paid to GaP, and a new model for excess absorption occurring inn‐type samples of this compound and in Si, GaAs, and AlSb is suggested. The application of similar techniques to PbS, PbSe, and PbTe is discussed, and results of electrical and optical measurements of energy gap and electron and hole mobilities presented.