Phase transitions in InSb were studied with use of energy-dispersive x-ray diffraction with a synchrotron source to pressures of 66 GPa. InSb transformed from the quasi-fourfold-coordinated zinc-blende structure to a quasi-sixfold-coordinated orthorhombic structure [InSb(IV)] at 2.5 GPa. Previous workers have claimed that the structure of orthorhombic InSb(IV) is disordered with space group Pmm2. From the results of recent theoretical calculations, we suggest that the structure of InSb(IV) is ordered and has space group Amm2. Around 6 GPa, InSb transformed to another phase which subsequently continuously transformed to a quasi-eightfold-coordinated hexagonal structure. Upon a further increase in pressure to 283 GPa, the sample transformed to an eightfold-coordinated cubic CsCl-type structure (if ordered) or to a bcc structure (if disordered). The structure remains cubic to at least 66 GPa, the highest pressure attained in this study. Both the hexagonal phase and the cubic phase are new phases of InSb. On the basis of theoretical calculations, all of these structures are expected to be ordered. The similarities between this phase-transition sequence in InSb and those of other III-V compounds as well as the isoelectronic element Sn are also discussed. © 1989 The American Physical Society.