Increasing power densities in Field Programmable Gate Arrays (FPGAs) have made them susceptible to thermal problems. The advent of platform FPGAs has further exacerbated the problems by increasing the power density variations on the FPGA fabric. Therefore, we need to characterize the die temperature of platform FPGAs. In this paper, we first estimate the temperature distribution within a Virtex-4 FPGA by feeding the block power numbers in an architecture-level temperature simulator calibrated to reflect a real FPGA package. We analyze the impact of different hard-wired blocks on the temperature profile, and observe that they introduce intra-die variation in temperature of up to 20°C. Next, we evaluate the influence of placement on temperature. Our experiments indicate a decrease in peak temperature by changing the placement of hard blocks, especially the high-speed transceivers. We further propose an iterative placement technique to reduce the peak temperature, and apply it on real designs. Finally, we propose alternate organizations of the hard blocks in the FPGA fabric to reduce temperature.