An experimental investigation of the stable generation of ultrashort optical pulses is reported by using a low-cost, uncooled Fabry-Perot (FP) semiconductor laser under the gain-switching operation. The timing jitter of gain-switched optical pulses is reduced by use of external continuous-wave (CW) light injection. The results show that an uncooled gain-switched FP laser can feasibly produce the stable optical pulse trains with pulse width of 26 ps and timing jitter as low as 400 fs at the repetition frequency of 2.5 GHz, when the injection power of an external CW light is appropriately chosen.