The paper reports the fabrication and gain measurements of buried facet optical amplifiers. Chip gain of 25 dB, gain ripple of < 1 dB and gain difference of < 1 dB for TE and TMpolarised light are observed. The gain is found to decrease rapidly with increasing temperature. This behaviour is explained using a model calculation of the radiative and nonradiative recombination rates in the active region of the amplifier.