Low-frequency, low-noise, low-power cryogenic electronics to read out photodetectors is being investigated for the star-tracking telescope of the Gravity Probe B spacecraft. We report additional results in evaluating low-frequency '1/f' noise of commercial and non-commercial GaAs field-effect transistors (FETs) at room and liquid-helium temperatures. No correlation was found between noise at these two temperatures. For our dc biasing conditions, the lowest- noise non-commercial GaAs FETs give a typical value of Kf (equals Af x gate area) approximately equals 2 X 10-22 V2 (DOT) m2; this corresponds to a noise voltage of approximately equals 80 nV/Hz1/2 at 1 Hz for a gate area of 3 X 104 micrometers 2, only a factor of approximately equals 3 higher than the best Si JFETs of comparable gate area operated at their optimum temperature. RTSs (random telegraph signals) were observed for many GaAs MESFETs at 4 K, for gate areas up to approximately equals 5000 micrometers 2. We also examined low-frequency '1/f' noise in relation to FET materials, processing, and pinch- off voltage but the results were inconclusive.