A design and simulation of a fully CMOS compatible micromachined multilayer cantilevers-based environmental thermometer are presented. The operation principle of the structure is depending on the mismatch effect of thermal expansion coefficient and the piezoresistive effect of polysilicon in CMOS process. Upon temperature variation, the deformation of the multilayer cantilever resulted from the large thermal expansion coefficient mismatch of different materials can be sensed and translated to an electrical voltage output by using a symmetric piezoresistive Wheatstone bridge. The mechanical characteristics of the device are analyzed with the extension of bi-layer Timoshenko model and the output of the read-out circuit is also simulated. The calculation and simulation show that the device with bi-direction deformation may have wide temperature range from -100 to 100°C and sensitivity about 0.15mV/°C, which fit the demand of radiosonde for environmental temperature measurement. This sensor may also have other favorable features, such as micro size, low-cost due to its working principle and compatibility with commercial CMOS process.