A numerical analysis is presented for buoyancy driven flow of a Newtonian fluid contained in a two dimensional (R, phi) hemispherical enclosure for high Rayleigh (Ra) numbers. It is assumed that the flow is driven by the uniformly distributed internal heat sources within the enclosure. All walls of the cavity are maintained at a constant temperature. Finite volume based SIMPLER algorithm has been used for the present analysis. Discretised governing equations, in primitive variables, are solved by a combination of Three Diagonal Matrix Algorithm (TDMA) and Point Successive Overrelaxation (PSOR) method. A benchmark solution prepared for a Ra number range of 10(7) to 10(12) and Prandtl (Pr) number 7.0, shows an excellent agreement with the experimental results obtained from the open literature.