By using standard CMOS processes and bulk micromaching technology, a uncooled infrared microbolometer detector based on the temperature character of the lateral polysilicon p +p -n + junction was developed. The temperature characteristic of the polysilicon p +p -n + junction's foreword bias were analyzed in detail. The theoretic expression and experimental data of the temperature rate of change of forward voltage drop were presented. The design ideas and fabrication processes were given. The temperature coefficient of the foreword voltage at a constant current is 1.5mV/K at various temperatures in the range of 284K to 253K. The responsivity and detectivity (D *) are 5.7×10 3V/W and 1.2×10 8cm.Hz 1/2 .W -1 in 3～5μm IR radiation band, respectively.