In this paper, a finite element formulation based on first-order shear deformation theory (FSDT) is used to study the thermal buckling behavior of functionally graded material (FGM) hemispherical shells with a cut-out at apex in a high temperature environment. A Fourier series expansion for the displacement variable in the circumferential direction is used to model the FGM hemispherical shell. The material properties of FGM hemispherical shells are functionally graded in the thickness direction according to a volume fraction power law distribution. Temperature-dependent material properties are considered to carry out a linear thermal buckling analysis. The hemispherical shell is assumed to be clamped-clamped and has a high temperature specified on the inner surface while the outer surface is at ambient temperature. The one-dimensional heat conduction equation is applied along the thickness of the shell to determine the temperature distribution and thereby material properties. Converged critical buckling temperatures are computed for two cases of thermal loads, namely, under uniform temperature rise and temperature gradient across the thickness. Numerical studies include the influence of, power law index, base to radius ratios, and different cut-out angles at the apex on the magnitude of thermal buckling temperature. © World Scientific Publishing Company.