FGH96 alloy is a nickel-based superalloy that is commonly used in fabricating the turbine disks of aero engines owing of its excellent mechanical properties. Because the properties of nickel-based superalloys are determined based on their microstructure, researchers have been studying the evolution of microstructure in FGH96. However, most studies have focused on FGH96 superalloys that have undergone a hot isostatic pressing (HIP) process or a combination of HIP and hot isostatic forging. Recently, hot extrusion (HEX) has been widely used for manufacturing FGH96 superalloys; however, the research on alloys manufactured via HEX is scarce. In this study, FGH96 superalloys were solution heat-treated at temperatures ranging from 1100 ^oC to 1260 ^oC, and the evolution of their microstructure was analyzed via OM, EBSD, and TEM techniques. The mechanism of static recrystallization and the formation mechanism of Σ3 twin boundaries were also investigated. The results showed that the static recrystallization grain size and grain boundaries, including small angle boundaries, large angle boundaries, and Σ3 twin boundaries, were substantially influenced by the solution temperature. Furthermore, a distinct correlation existed between the microstructure evolution and solution temperature. The static recrystallization in the FGH96 alloy mainly occurs through the nucleation and growth of subgrains at temperatures ranging from 1100 ^oC to 1260 ^oC. During the static recrystallization process, a large number of stacking faults formed at the (\mathrm{11}\overline{\mathrm{1}}) close-packed plane, which improved the free energy. Therefore, to reduce the free energy, subsequent atoms were stacked symmetrically to the stacking faults, leading to the formation of Σ3 twin boundaries.