Experiments were performed on natural convection heat transfer from circular pin fin heat sinks subject to the influence of its geometry, heat flux and orientation. The geometric dependence of heat dissipation from heat sinks of widely spaced solid and hollow/perforated circular pin fins with staggered combination, filled into a healed base of fixed area is discussed. Over the tested range of Rayleigh number, 4.5 x 106≤Ra≤1.65 x 107it was found that the solid pin fin heat sink performance for upward and sideward orientations shows a competitive nature, depending on Rayleigh number and generally shows a higher heat (transfer coefficients than those of the perforated/ hollow pin sin ones in both arrangements. For all tested hollow/perforated pin fin heat sinks, however, the performance for sideward facing orientation was better than that for upward facing orientation. This argument is supported by observing that the augmentation factor was around 1.05-1.11, depending on the hollow pin diameter ratio, DVD, Meanwhile, the heat sink of larger hollow pin diameter ratio, DID offered higher heat transfer coefficient than that of smaller Di/DO for upward orientation, and the situation was reversed for sideword orientation. The heat transfer performance for heat sinks with hollow/perforated pin fins was better than that of solid pins. The temperature difference between the base plate and surrounding air of these heat sinks was less than that of solid pin one and improved with increasing Di/DO.