The invention provides a label-free sensor that includes a substrate, a first electrode formed on the substrate, a second electrode formed on the substrate and spaced away from the first electrode, and a semiconductor layer formed on the substrate and being in contact with the first electrode and the second electrode. The semiconductor layer has a plurality of probe groups bonded to the semiconductor layer by functionalization, for sensing a coupling-specific substance having bonding specificity with the probe groups. The semiconductor layer is bonded with the probe groups, and the detection of detected object is performed in an instant, quick, rapid, and sensitive manner by measuring variation in electric current, avoiding the use of fluorescent reading equipment for reading fluorescent signals.