Organic field-effect transistors (OFETs) are promising electronic devices owing to their attractive features such as a low cost, solution processability, and ease of use. In this regard, we have fabricated extended-gate-type OFETs functionalized with natural molecular recognition materials as biosensors for the detection of biomarkers. Toward the development of a potential psychological stress monitoring method based on OFETs, we have successfully detected three types of psychological stress biomarkers: chromogranin A (CgA), immunoglobulin A (IgA), and nitrate (NO₃⁻). The OFETs reproducibly respond to the biomarkers, demonstrating their ability to detect potential psychological stress in individuals. Notably, the detectability of the OFETs makes them suitable for the analyses of real samples. Thus, we strongly believe that the developed system based on extended-gate-type OFETs could be employed as a sensor platform for biosensor applications in the field of healthcare.