Coupled conduction and natural convection heat transfer has been investigated numerically for protruding heat sources mounted to one vertical wall of a rectangular cavity. The heat sources simulate an array of computer chips mounted on a substrate of finite thermal conductivity. The back of the substrate and the horizontal walls of the cavity are assumed to be adiabatic, while the opposing vertical wall provides an isothermal heal sink. The fluid Prandtl number and the heater/fluid thermal conductivity ratio are fixed at 25 and 2350, respectively, corresponding to a dielectric fluid (FC-77, manufactured by 3M Company) and silicon chips. With increasing modified Rayleigh number (104 < Ra*LZ < 109), the cavity flow approaches boundary layer behavior, and more fluid penetrates the regions between protrusions. The effect of contact resistance between the heater and substrate is shown to be small for Rnth < 10 cm2 °C/W. With decreasing substrate thermal conductivity [1.48 W/ (m K) <. Ks < 148 W/(m K)], fluid circulation decreases and the maximum heater temperatures increase.