A memory device includes a memory unit comprising a substrate supporting mobile charge carriers. Insulative features formed on the substrate surface define first and second substrate areas on either side of the insulative features areas being connected by an elongate channel defined by the insulative features. The memory unit is switchable between first and second states in which the channel respectively provides a first conductance and a second, different conductance between the first and second areas at a predetermined potential difference between said first and second. A write circuit is arranged to apply a first potential difference across the first and second areas for changing the memory unit to the first state, and a second, different potential difference for changing the memory unit to the second state. A read circuit is arranged to apply the predetermined potential difference across the first and second areas for reading the state.