This paper describes experimental results on low frequency noise in several types of polysilicon‐emitter NPN bipolar junction transistors. The experimental data were modelled using a combination of 1/fnoise, generation‐recombination noise (g‐r), and shot noise, and good agreement between model calculations and experimental measurements were obtained. Observed differences in the experimental low frequency noise spectra of devices with similar geometry and under similar biasing conditions could be explained by the differences in the generation‐recombination (g‐r) noise contributions. Experiments were performed on devices with emitter areas varying from 1.6 to 144 &mgr;m2, and it was found that the magnitude of the flicker noise contributionKFvaried inversely with emitter areaAEor emitter perimeterPE. The fact thatKF∼A−1EorKF∼P−1Eis explained by the observation thatAE∼PEwithin fabrication errors/tolerances. Using a set of 3.2 &mgr;m2BJTs with pronounced g‐r noise, input current noise was measured at different temperatures and from a deconvolution of the noise spectra, a trap at ∼400 meV and with a capture cross section of ∼4×10−17cm2was identified. Finally, the effect of different base implant and rapid thermal annealing conditions, polysilicon emitter thicknesses, and surface etching conditions on the noise magnitude were studied, and these results are also reported. ©1995 American Institute of Physics.