Tunability of the cw radiation from a GaAs injection laser in an external dispersive cavity was achieved over a range of 150 Å about a center wavelength of 8525 Å at 77°K. The emitted radiation was analyzed with a Fabry‐Perot etalon. Under certain conditions single‐mode operation with cw output power as large as 17 mW was observed. Half‐width of such modes was estimated to be less than 350 MHz.