An ISFET pH meter is composed of an ISFET sensor[1], an ISFET readout circuit, a temperature sensor, a temperature readout circuit, a microcontroller with a built in ADC and a LCD for displaying results. The ISFET sensor and temperature sensor measure the pH and the temperature of the solution respectively. The temperature sensor and temperature readout circuit serve as an integral part of microcontroller-based ISFET pH meter system. Both provide temperature monitoring for the automatic compensation of temperature effects on pH meter readings. This study presents a temperature sensor with a readout circuit using CMOS technology.The temperature sensor consists of two elements, a PTAT generator[2], and an operational amplifier server as buffer[3]. It was implemented in an integrated circuit based on TSMC 0.35 µm 2P4M CMOS technology that operates on a single rail 3.3V power supply. Its core area is 357.3µm by 135.05µm and has an average power dissipation of 495.4614 µW in typical case. The temperature sensor operates with a resolution of 5mV/oC. Post-layout simulation showed a linear output voltage from 0oC to 100oC.