Provided is a sensor having a high sensitivity and a high degree of freedom of layout by reducing constrictions of the channel shape, the reaction field area, and the position. Provided is also a method for manufacturing the sensor. The sensor (10) includes: a source electrode (15), a drain electrode, (14), and a gate electrode (13) arranged on silicon oxide film (12a, 12b); a channel (16) arranged on the silicon oxide films (12a, 12b) and electrically connected to the source electrode (15) and the drain electrode (14); and a reaction field (20) arranged on the silicon oxide films (12a, 12b). The reaction field (20) is formed at a position on the silicon oxide film (12a), the position being different from a position for the channel (16). With this configuration, it is possible to independently select the shape of the channel (16) and the area of the reaction field (20). This enables the sensor (10) to have a high measurement sensitivity and a high degree of freedom of layout.