Abstract To understand how biological neural networks, such as the retina, process information, transparent microelectrode arrays have been made using the semiconductor indium tin oxide (ITO). These arrays have been used for in vitro biological experiments where it is possible to record simultaneously the action potentials from hundreds of retinal ganglion cells. To combat inefficient detection of a particular class of retinal output neuron, an array with 30 μ m spaced 519-electrodes has been developed. These arrays are characterised electrically before being employed in biological experiments. With a view to future higher density arrays, impedance and capacitance measurements were made over varying width, length and separation of ITO wires. These tests led to an equivalent circuit model representing electrode array characteristics. The results suggest array sizes of 2000 electrodes and beyond should be feasible.