The numerical simulation on the three-dimensional natural convection heat transfer in the enclosure with heat generating chip is performed, and the effects of convective heat loss and vents are also examined. The effects of the Rayleigh number and outer Nusselt number (Nu$_{0}$) on the maximum chip temperature and the fractions of heat loss from the hot surfaces are investigated. The results show that conduction through the substrate is dominant in heat dissipation. With the increase of Rayleigh number, heat dissipation through the chip surfaces increases and heat loss through the substrate decreases. Maximum dimensionless temperature with vents is found to decrease about 40% compared to the one without vents at Nu$_{0}$=0.l. It is also shown that effects of size and location of the vents are negligible.ble.