The formation and analyses of thin film Ag/AgCl reference electrode by two different methods were studied with aim to extend the lifetime and to determine the potential stability over time. To convert part of thin Ag film into AgCl, chemical formation in FeCl3 of different molarities and electrochemical formation in solution of 3 M NaCl were employed. Optical and SEM analyses of formed Ag/AgCl microstructure revealed that both methods result in uniform distribution of polycrystalline grains with size between 1-3 micrometers. Potential stability measurements were performed by measuring the potential of thin film reference electrode against standard calomel liquid junction electrode. When measuring potential difference in high molarity electrolyte (3 M NaCl), lifetime of thin film electrodes was found to be limited to few hours, though in weak solutions it can be maintained up to several days. Preliminary results showed good potential stability (<;1% change per hour). It was shown that additional passivation of AgCl layer by a thin PDMS layer significantly increased the lifetime of the electrode.