The probability distribution of electrical characteristic parameters of semiconductor device is an important reference which is used to analyze the reliability and quality consistency of devices. These distributions are considered as normal distribution at home and abroad. This paper utilized mature GaAs MESFET low noise amplifier as analytic sample which is volume production and wide application, and used high-precision Agilent B1505A device analyzer to test main electrical characteristics of 408 samples. After the distribution generation of test results, the Skewness-Kurtosis method was used to analyze probability distributions of the results. At last, the conclusion of distribution of measuring parameter is non-normal distribution was educed.