A procedure for precision fitting of resolution distorted beta spectra, using shape factor parameterization, is described. A derivation of the fitting function is made, and a method for decoupling the fitting parameters is discussed. This decoupling allows the spectrum intensity, endpoint, and shape factor parameters to be determined with a high degree of precision. This method is applicable to multigroup spectra with components having an arbitrary degree of forbiddenness, unique or non-unique. Included is a description of a computer program which is designed to use this method in the analysis of spectra measured with a 4π semiconductor spectrometer. Numerous methods of least squares minimization have been tried, and two methods of error analysis are discussed. Some results from the analysis of 36Cl, 143Pr, 185W are given.