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Hooge's empirical equation for the 1/f noise of resistors has been shown to be described by temperature fluctuations and Hooge's parameter was shown to be simply related to the ratio of the total number of conduction electrons and total number of atoms in the sample. At low frequencies the mean square temperature fluctuation around the average temperature depends on the diffusion transit time to the heat sink and inversely on the number of atoms in the sample. At higher frequencies temperature fluctuations are attenuated by the heat capacity of the sample which results in the 1/f frequency dependence of temperature fluctuations. Here the results for these temperature fluctuations are applied to describe the 1/f noise of bipolar transistors. In bipolar transistors the current is an exponential function of temperature so the noise is easier to observe and measure.