This thesis devotes to develop a wafer-level packaging technique of the planar AgCl-based micro reference electrode and to investigate its various electrochemical characteristics (including the potential stability and offset voltage, AC impedance, cyclic-voltammetry analysis, electrochemical noise and reproducibility). The miniaturized all-solid-state reference electrode can integrated with many biomedical or biochemical sensors for substantially reduce the dimension of the whole sensing system and improve the commercial capability of portable detecting products. This study reports firstly a smallest module of the micro reference electrode with dimension only about 9 mm (L) ¡Ñ 6 mm (W) ¡Ñ 1 mm (H) in the worldwide using the silicon bulk-micromachining technology, thin film deposition and chloridation techniques. The packaged reference electrode module is constructed by two bonded wafers with different functions. One wafer of this module is defined as ¡§electrode chip¡¨ and it has a Ti/Pd/Ag/AgCl planar quasi-reference electrode deposited on its surface. Another wafer is called as ¡§packaging chip¡¨ and it has two bulk-micromachined silicon cavities for the filling/sealing of 1.33 ~ 6.40 £gL KCl-gel (as the salt-bridge of electrode) and electrical connection. Many electrochemical characteristics of the encapsulated solid-state micro reference electrode are tested and improved for the commercial applications. Including a very stable cell potential (<4 mV in 30000 sec.), an approximately zero offset-voltage, a low AC impedance (1~20 K£[), and high reproducibility (drift less than 3~8 mV in 30000 sec. and the range of offset voltage is -6 ~ 3 mV) of the packaged micro reference electrode are demonstrated. Furthermore, stable CV curve of the packaged Ti/Pd/Ag/AgCl/KCl-gel reference electrode were proved by cyclic-voltammetry analysis and its low electrochemical noise spectrum was investigated and discussed in this work. Compared with the commercial reference electrode, the planar miniaturized AgCl reference electrode module developed in this thesis has displayed its many excellent characteristics and with a dimension only 250 times smaller than the conventional reference electrode.