Amplified spontaneous emission has been observed in a new semiconductor oligomer of 2-decyl-6-{[4'-(naphthalene-1-yl-phenylamino)-biphenyl-4-yl]-[4-(naphtha lene-1-yl-phenyt-amino)-phenyl]-amino}-benzo[de]isoquinoline-1,3-dione (4-triarylamine substituted 1,8-naphthalimide TAANPI) doped polymer films pumped by the second harmonic of a Nd:YAG laser. The dependence of the threshold and gain on the oligomer concentration in polymer was studied in detail. It was found that the semiconductor oligomer shows low threshold, high gain and low loss even though the doped oligomer concentration is up to 60%, indicating a low concentration quenching effect. This demonstrates that the oligomer could be a promising candidate as gain medium for organic diode lasers. (c) 2005 Elsevier B.V. All rights reserved.