A reconfigurable field-effect transistor (RFET) with memory functionality is proposed as a new high-density synaptic device capable of exclusive NOR (XNOR) operation for a binary neural network (BNN). A RFET with three gates is used in this letter, consisting of two program gates (PGs) electrically connected to each other and a control gate (CG) between the PGs. By changing the polarity of the PG bias or the polarity of the charge trapped in Si3N4 layer on the PGs, the RFET operates as an ${n}$ - or a ${p}$ -MOSFET having a CG as a switching gate. The XNOR operation is successfully demonstrated in a fabricated RFET. The on/off current ratio (the ratio of 1 to 0 in the result of the XNOR operation) is ~104 and the current is ~1 nA/ $\mu \text{m}$ . Using a RFET as a synaptic device for a BNN is efficient in terms of the area (~8F2/synapse) because XNOR operation can be performed using only one RFET.