This paper presents a new VHDL-AMS behavioral model of an electrochemical cell suitable for the design of VLSI bio-chips. Existing models are mainly equivalent circuit macromodels using electrical primitives, which hardly fit the actual behavior of biosensors. The presented VHDL-AMS model expresses a more realistic behavior as it can directly use electrochemical equations. It can also be made very flexible and reusable for different experimentation cases. Last, but not least, it can be easily used for the design of bio-chips.