The frequency of an AlGaAs diode laser has been stabilized to the center frequency of the optogalvanic signal corresponding to the 4s′01–4p12(Racah notation) transition of Ar I at 8408.2094 A˚. The first derivative curve of the line was used as the error signal to be fed back to the operating current source of the diode laser. Fluctuation of the laser frequency was within 200 kHz for several hours.