Part I of this investigation involves theoretical and experimental characterization of the noise performance of modern silicon planar bipolar junction transistors (BJT's) above the 1/f noise frequency region in a temperature range of 60-300 K and for several difference bias conditions. At temperatures below approximately 110 K, an excess noise source as measured by the equivalent noise resistance RN, referred to the input of the device, common-base configuration, is revealed. This excess source, resulting from a generation-recombination process within the base region of the device, is shown to have a linear dependence on the base current and base resistance as KIB2rb'b2, and an exponential dependence on temperature.