Proportional to absolute temperature (PTAT) BiCMOS integrated temperature sensor was designed by applying the index characteristics of a MOSFET transistor saturated drain current, which worked on weak inversion region.The main circuit was composed by three parts, which were PTAT current generating circuit, start up circuit and output circuit. The circuit had the advantages of simple structure and small volume. The tested results indicated that the accuracy of the integrated temperature sensor was within 0.5 ℃,the linearity was within 0.65% , the sensitivity was 2.5 μA/℃and the area of the chip was 150 m×75 m The integrated temperature sensor had higher linearity and sensitivity which could be widely applied to various kinds of portable electronic products.