The present invention concerns a biosensor (1) comprising: a source element (13); a drain element (17); a semiconductor channel element between the source element (13) and the drain element (17) for forming an electrically conductive channel with adjustable conductivity between the source and drain elements; a first gate element (3, 5) configured to be electrically biased to set a given operational regime of the sensor (1) with given electrical conductivity of the channel; and a second gate element (7), physically separate from the first gate element (3, 5), configured to be in contact with a solution comprising analytes allowed to interact with a gate contact surface of the second gate element (7) to generate a surface potential change dependent on the concentration of the analytes in the solution. The channel element (21) is substantially fully depleted allowing the first and second gate elements (3, 5, 7) to be electrostatically coupled such that the surface potential change at the second gate element (7) is configured to modify the electrical conductivity of the channel.