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This paper presents a novel differential current mode readout circuit for the ion sensitive field effect transistor (ISFET) as a pH sensor. It uses two second generation current conveyers (CCII), and provides an output current that is linearly sensitive to pH over a wide range (pH 2-12). It is more suitable for A/D conversion compared to voltage output circuits. The circuit is operating in differential mode, reference field effect transistor (REFET) is used to realize temperature compensation. The proposed readout circuit has simple structure, it uses only one type of active element (i.e. CCII), so that, it can be easy integrated on one chip and fabricated using a conventional CMOS process. Simulation results demonstrate the proposed circuit is well working and can be suitable used as an ISFET pH sensor readout circuit.