A new overheat protection circuit , a thermal regulator , was presented , in which temperature variation caused by power dissipation was confined to a closed2loop. Thus a negative thermal feedback was formed , which regulated the output current to maintain a constant die temperature during high power operation , or under high am2 bient temperature conditions , to maximize the output power without risk of overheating. The circuit was implemen2 ted in SMIC’s 0. 13μm CMOS logic process. Test result s showed that the chip temperature can be maintained con2 stant at 105 ℃.