s We demonstrate optically excited lasing by an organic semiconducting thin-film based on 2,7-bis[4-(N-carbazole)phenylvinyl]-9,9'-spirobifluorene (spiro-SBCz) as an active gain medium with a first-order distributed feedback (DFB) reflector. We prepared DFB reflectors with periods from 132.5 to 145.00 nm and grooves from 70 to 140 nm depth by using electron-beam-lithography and plasma-etching techniques. The laser having a reflector with a 145.0 nm period had a lasing threshold of 0.72 +/- 0.07 mu J/cm(2), 83% lower than its threshold of amplified spontaneous emission (4.1 +/- 0.4 mu J/cm(2)).