Thermal convection resulting from a temperature difference between two vertical surfaces of a square cavity is considered. The effects of a semicylindrically shaped protuberance, located at the bottom of the cavity, on total and local heat transfer rates are examined numerically. The numerical results are for a Prandtl number of 0.71 and for Rayleigh numbers up to 104. The results show that the presence of the protuberance leads to a decrease in heat transfer rates in the lower part of the cavity. This relative decrease initially becomes more pronounced as the Rayleigh number increases, but is less significant as the Rayleigh number increases past a critical value. This critical Rayleigh number depends on the radius of the protuberances and its value increases as the radius increases. These results are in general agreement with those found in other investigations dealing with the effects of partitions.