A thermal model was developed to investigate the effect of multi-core microprocessor circuit layout on thermal performance. Die size of 20 mm times 20 mm and power dissipation of 200W were assumed in the model. A high thermal conductivity heat spreader of 50mm times 50 mm times 2 mm and air-cooled heat sink base of 100 mm times 100 mm times 5 mm were employed for the model. The study begins with single core chip layout. Several variables including CPU power level, local hot spot power density, hot spot location and hot spot size were evaluated in the simulation. Thereafter, thermal performance of a multi-core processor with multiple hot spots in a single chip was simulated at various distributions, hot spot sizes, and number of hot spots. Thermal performance comparison was made between single core and multi-core architectures on a single chip. Finally general thermal guidance is given for the circuit design