Human blood reflects the health of internal organs and tissues, the constituent can be affected on account of abnormal health status. Moreover, the ion concentration of chloride and ammonium in human blood relates to the functionality of our kidney and liver, which is one of the most important health indicators. For real-time monitoring and detecting applications, this study uses micro-electromechanical systems (MEMS) surface micromachining process technology to develop an extended-gate field-effect transistors (EGFET), and by combining two different ion-selective membranes (ISM), a disposable silicon-based chloride and ammonium micro ion sensor was fabricated. The main process steps include four photolithography process and two thin film deposition. In order to probe into the influences on modulating three designing parameters: (i) channel width to length ratio; (ii) channel shape; (iii) mixing ratio of the sensing film additives, the size of the sensing area is fixed to 1¡Ñ1 mm2 while the device is fixed to 6 mm3. In this thesis, the optimization of the development chloride and ammonium micro ion sensors, according to the measuring results from the commercial semiconductor analyzer (Agilent B1500A), when measuring range of 10-1~10-5 mol/L, the sensitivity and linearity for the chlorine ion sensor is 47.5 mV/pCl and 99.13%, as for the ammonium ion sensor are 41.2 mV/pNH4 and 99.28%, the interfering ion selectivity coefficients (log KCl,OH, log KNH ,Na) are -4.71 and 0.53 respectively.